Wikipedia

COVID-19 vaccine clinical research

(Redirected from Pharmacovigilance of the COVID-19 vaccines)

Further information: COVID-19 vaccine

COVID-19 vaccine clinical research uses clinical research to establish the characteristics of COVID-19 vaccines. These characteristics include efficacy, effectiveness, and safety. As of November 2022, 40 vaccines are authorized by at least one national regulatory authority for public use:[1][2]

As of June 2022, 353 vaccine candidates are in various stages of development, with 135 in clinical research, including 38 in phase I trials, 32 in phase I–II trials, 39 in phase III trials, and 9 in phase IV development.[1]

Formulation

A wide variety of technologies are being used to formulate vaccines against COVID-19. The development and deployment of mRNA vaccines and viral vector vaccines has been outstandingly rapid and can be described as revolutionary. However, global vaccine equity against COVID-19 has not been achieved. Conventional vaccine manufacturing approaches using whole inactivated virus (WIV), protein-based subunit vaccines, and virus-like particles (VLPs) may offer advantages in the development of vaccines for use in low- and middle-income countries (LMICs) and in addressing vaccine access gaps.[6]

Many vaccine candidates use adjuvants to enhance immunogenicity, as part of the delivery system or as an accompanying immune stimulant.[8][9] Vaccine adjuvant formulations using aluminum salts or "alum" may be particularly effective for technologies using inactivated COVID-19 virus and for recombinant protein-based or vector-based vaccines.[6][10]

Status

Clinical trials

Main article: Clinical trial

The clinical trial process typically consists of three phases, each following the success of the prior phase. Trials are doubly blind in that neither the researcher nor the subject know whether they receive the vaccine or a placebo. Each phase involves randomly-selected subjects who are randomly assigned to serve either as recipients are controls:

  • Phase I trials test primarily for safety and preliminary dosing in healthy subjects. Dozens of subjects.
  • Phase II trials evaluate immunogenicity, dose levels (efficacy based on biomarkers) and adverse effects.[11][12] Hundreds of subjects. Sometimes Phase I and II trials are combined.[12]
  • Phase III trials typically involve more participants at multiple sites, include a control group, and test effectiveness of the vaccine to prevent the disease (an "interventional" or "pivotal" trial), while monitoring for adverse effects at the selected dose.[11][12] Safety, efficacy, and clinical endpoints may vary, including the definition of side effects, infection or amount of transmission, and whether the vaccine prevents moderate or severe infection.[13][14][15]

A clinical trial design in progress may adopt an "adaptive design". If accumulating data provide insights about the treatment, the endpoints or other aspects or the trial can be adjusted.[16][17] Adaptive designs may shorten trial durations and use fewer subjects, possibly expediting decisions, avoiding duplication of research efforts, and enhancing coordination of design changes.[16][18]

Vaccine candidates in human trials

The table below shows various vaccine candidates and the phases which they had completed per the references. Current phases are also shown along with other details.

COVID-19 candidate vaccines in Phase I–III trials
COVID‑19 vaccine candidates in Phase I–III trials[19][20][21]
(
)
Vaccine candidates,
developers, and sponsors 		Country of origin Type (technology) Current phase (participants)
design 		Completed phase[a] (participants)
Immune response 		Pending authorization
Sanofi–GSK COVID-19 vaccine (VAT00008, Vidprevtyn)
Sanofi Pasteur, GSK 		France, United Kingdom Subunit (SARS-CoV-2 S adjuvanted recombinant protein) Phase III (37,430)[22][23]
A Parallel-group, Phase III, Multi-stage, Modified Double-blind, Multi-armed Study to Assess the Efficacy, Safety, and Immunogenicity of Two SARS-CoV-2 Adjuvanted Recombinant Protein Vaccines (Monovalent and Bivalent) for Prevention Against COVID-19 in Adults 18 Years of Age and Older.
May 2021 – Mar 2023, Colombia, Dominican Republic, Ghana, Honduras, India (3,000), Japan, Kenya,[24] Mexico,[25] Nigeria, Pakistan, Sri Lanka, Uganda, United States 		Phase I–II (1,160)
Phase I-IIa (440): Immunogenicity and Safety of SARS-CoV-2 Recombinant Protein Vaccine Formulations (With or Without Adjuvant) in Healthy Adults 18 Years of Age and Older.[26]
Phase IIb (720): Immunogenicity and Safety of SARS-CoV-2 Recombinant Protein Vaccine With AS03 Adjuvant in Adults 18 Years of Age and Older.[27]
Sep 2020 – Apr 2022, United States
Emergency (5)
Nanocovax[34]
Nanogen Pharmaceutical Biotechnology JSC 		Vietnam Subunit (SARS‑CoV‑2 recombinant spike protein with aluminum adjuvant)[35][36] Phase III (13,000)[37][38]
Adaptive, multicenter, randomized, double-blind, placebo-controlled
Jun 2021 – Jul 2022, Vietnam 		Phase I–II (620)[39]
Phase I (60): Open label, dose escalation.
Phase II (560): Randomization, double-blind, multicenter, placebo-controlled.
Dec 2020 – Jun 2021, Vietnam
Emergency (1)
UB-612
United Biomedical,Inc, Vaxxinity, DASA 		Brazil, Taiwan, United States Subunit (Multitope peptide based S1-RBD-protein based vaccine) Phase III (18,320)[41][42]
Phase IIb/III (7,320): Randomized, Multicenter, Double-Blind, Placebo Controlled, Dose-Response.
Phase III (11,000)
Jan 2021 – Mar 2023, Taiwan (phase 2b/3), India (phase 3)[43] 		Phase I–II (3,910)[44]
Phase 1 (60): Open-label study
Phase IIa (3,850): Placebo-controlled, Randomized, Observer-blind Study.
Sep 2020 – Jan 2021, Taiwan
Emergency (1)
SCB-2019[46][47]
Clover Biopharmaceuticals,[48][49] Dynavax Technologies,[50] CEPI 		China Subunit (spike protein trimeric subunit with combined CpG 1018 and aluminium adjuvant) Phase III (30,300)
Phase II/III (30,000): Randomized, double-blind, controlled.
Phase III (300): Double-blind, randomized, controlled.[51]
Mar 2021 – Oct 2022, Belgium, Brazil, Colombia, Dominican Republic, Germany, Nepal, Panama, the Philippines, Poland, South Africa, Ukraine 		Phase I–II (950)
Phase I (150): Randomized, Double-blind, Placebo-controlled, First-in-human.
Phase II (800): Multi-center, Double-blind, Randomized, Controlled.[52]
Jun 2020 – Oct 2021, Australia (phase 1), China (phase 2)
Emergency (1)
S-268019
Shionogi 		Japan Subunit Phase III (54,915)[53][54]
Phase II/III: Open-label.
Phase III: Randomized, observer-blind, placebo-controlled cross-over.
Oct 2021 – Dec 2022, Japan (3,100), Vietnam 		Phase I–II (300)[55]
Randomized, double-blind, placebo-controlled, parallel-group.
Dec 2020 – Aug 2021, Japan
West China Hospital COVID-19 vaccine
Jiangsu Province Centers for Disease Control and Prevention, West China Hospital (WestVac Biopharma), Sichuan University 		China Subunit (recombinant with Sf9 cell) Phase III (40,000)[56]
Multicenter, randomized, double-blind, placebo-controlled.
Jun 2021 – Feb 2022, Indonesia, Kenya, Malaysia,[57] Mexico, Nepal, the Philippines (5,000)[58] 		Phase I–II (5,128)[59][60][61]
Phase I (168): Single-center, Randomized, Placebo-controlled, Double-blind.
Phase IIa (960):Single-center, Randomized, Double-Blinded, Placebo-Controlled.
Phase IIb (4,000):Single-center, Randomized, Double-Blinded, Placebo-Controlled.
Aug 2020 – May 2021, China
DelNS1-2019-nCoV-RBD-OPT (DelNS1-nCoV-RBD LAIV)
Beijing Wantai Biological Pharmacy, University of Hong Kong, Xiamen University 		China, Hong Kong Replicating viral vector (flu-based-RBD[clarification needed]) Phase III (40,000)[62]
Multi-center, Randomized, Double-blind, Placebo controlled.
Oct 2021 – Apr 2022, the Philippines 		Phase I–II (895)[63][64]
Phase I (60+115=175)
Phase II (720)
Sep 2020 – Sep 2022, China (60), Hong Kong (115)
Versamune-CoV-2FC [pt]
Farmacore Biotechnology, PDS Biotechnology Corporation, Faculty of Medicine of Ribeirão Preto 		Brazil, United States Subunit Phase III (30,000)[65]
Double-blind, randomized controlled.
Aug–Dec 2021, Brazil 		Phase I–II (360)[66][67][68]
Double-blind, randomized controlled.
Mar–Aug 2021, Brazil
Walvax COVID-19 vaccine (ARCoV)[69]
PLA Academy of Military Science, Walvax Biotech,[70] Suzhou Abogen Biosciences 		China RNA Phase III (28,000)[71]
Multi-center, Randomized, Double-blind, Placebo-controlled
May–Nov 2021, China,[72] Colombia, Indonesia, Malaysia, Mexico, Nepal, Pakistan, the Philippines, Turkey 		Phase I–II (908)
Phase I (168)
Phase II (420)
Phase I/II (320)[73]
Jun 2020 – Oct 2021, China[74]
V-01
Livzon Mabpharm, Inc. 		China Subunit (SARS-CoV-2 recombinant fusion protein) Phase III (22,500)[75]
Global, multi-center, randomized, double-blind, placebo-controlled.
Aug 2021–Mar 2023, the Philippines 		Phase I (1,060)[76][77]
Phase I (180): Single-center, randomized, double-blind and placebo-controlled.
Phase II (880): Randomized, double-blind, and placebo-controlled.
Feb–May 2021, China
ARCT-154 (VBC-COV19-154 in Vietnam)[78][79][80]
Arcturus Therapeutics, Vinbiocare 		United States, Vietnam RNA Phase III (20,600)
Phase IIIa (600): Randomized, double-blinded, placebo controlled.
Phase IIIb (20,000): Randomized, double-blinded, placebo controlled.[81][82]
Oct-Dec 2021, Vietnam 		Phase I–II (400)
Phase I (100): Randomized, double-blinded, placebo controlled.
Phase II (300): Randomized, double-blinded, placebo controlled.
Aug-Oct 2021, Vietnam[83]
ReCOV
Jiangsu Rec-Biotechnology Co Ltd 		China Subunit (Recombinant two-component spike and RBD protein (CHO cell)) Phase II–III (20,301)[84]
Multi-center, randomized, double-blind, placebo-controlled.
Dec 2021–Dec 2022, China, New Zealand, the Philippines 		Phase I (160)[85]
First-in-human, randomized, double-blind, placebo-controlled, dose-finding.
Jun–Dec 2021, New Zealand
BriLife (IIBR-100)[86]
The Israel Institute for Biological Research 		Israel Vesicular stomatitis vector (recombinant) Phase III (20,000)[87]
Randomized, multi-center, placebo-controlled.
Sept – Dec 2021, Israel 		Phase I–II (1,040)[88]
Randomized, multi-center, placebo-controlled, dose-escalation.
Oct 2020 – May 2021, Israel
Zhongyianke Biotech–Liaoning Maokangyuan Biotech COVID-19 vaccine
Zhongyianke Biotech, Liaoning Maokangyuan Biotech, Academy of Military Medical Sciences 		China Subunit (Recombinant) Phase III (14,600)[89]
International multicenter, randomized, double-blind, placebo-controlled.
Sep 2021–?, China 		Phase I–II (696)[90]
Phase I (216): Randomized, placebo-controlled, double-blind.
Phase II (480): Single-center, randomized, double blinded, placebo controlled.[91]
Oct 2020 – Jul 2021, China
GX-19 (GX-19N)[92][93][94]
Genexine consortium,[95][96] International Vaccine Institute 		South Korea DNA Phase II–III (14,000)[97]
Randomized, double-blinded, placebo-controlled.
Oct 2021 – Oct 2022, Indonesia, Seoul 		Phase I–II (410)
Phase I-II (170+210+30): Multi-center, some open-labeled, some double-blinded, single arm, randomized, placebo-controlled
Jun 2020 – Jul 2021, Seoul
GRAd-COV2[98][99]
ReiThera, Lazzaro Spallanzani National Institute for Infectious Diseases 		Italy Adenovirus vector (modified gorilla adenovirus vector, GRAd) Phase III (10,300)[100][101]
Randomized, stratified, observer-blind, placebo-controlled.
Mar–Oct 2021, Italy 		Phase I (90)[102]
Subjects (two groups: 18–55 and 65–85 years old) randomly receiving one of three escalating doses of GRAd-COV2 or a placebo, then monitored over a 24-week period. 93% of subjects who received GRAd-COV2 developed anti-bodies.
Aug–Dec 2020, Rome
Inovio COVID-19 Vaccine (INO-4800)[103][104]
Inovio, CEPI, Korea National Institute of Health, International Vaccine Institute 		South Korea, United States DNA vaccine (plasmid delivered by electroporation) Phase III (7,517)
Randomized, placebo-controlled, multi-center.[105]
Nov 2020 – Jan 2023, Brazil, Colombia, Mexico, the Philippines, United States[b] 		Phase I–II (920)
Phase Ia (120): Open-label trial.
Phase Ib-IIa (160): Dose-Ranging Trial.[106]
Phase II (640): Randomized, double-blinded, placebo-controlled, dose-finding.[107]
April 2020 – Feb 2022, China (phase II), South Korea (phase Ib-IIa), United States
DS-5670[108]
Daiichi Sankyo[109] 		Japan RNA Phase II–III (5,028)[110]
Randomized, Active-comparator, Observer-blind.
Dec 2021 – Jul 2023, Japan 		Phase I–II (152)[111]
A Phase 1/2 Study to Assess the Safety, Immunogenicity and Recommended Dose of DS-5670a (COVID-19 Vaccine) in Japanese Healthy Adults and Elderly Subjects.
Mar 2021 – Jul 2022, Japan
GBP510
SK Bioscience Co. Ltd., GSK 		South Korea, United Kingdom Subunit (Recombinant protein nanoparticle with adjuvanted with AS03) Phase III (4,000)[112]
Randomized, active-controlled, observer-blind, parallel-group, multi-center.[113]
Aug 2021-Mar 2022, South Korea 		Phase I–II (580)[114][115]
Phase I-II (260-320): Placebo-controlled, randomized, observer-blinded, dose-finding.
Jan–Aug 2021, South Korea
HGC019[116]
Gennova Biopharmaceuticals, HDT Biotech Corporation[117] 		India, United States RNA Phase II–III (4,400)[118]
A prospective, multicentre, randomized, active-controlled (with COVISHIELD), observer-blind study to evaluate safety, tolerability and immunogenicity in healthy adults.
Phase II (400)
Phase III (4,000)
Sep 2021 – Sep 2022, India 		Phase I–II (620)[119][120][121]
Randomized, phase I/II, placebo-controlled, dose-ranging, parallel-group, crossover, multi-centre study to evaluate the safety, tolerability and immunogenicity in healthy adult subjects.
Phase I (120) open-label study in healthy 18-70 year-olds.
Phase II (500) observer-blind study in healthy 18-75 year-olds.
Apr 2021 – Oct 2021, India
KD-414
KM Biologics Co 		Japan Inactivated SARS‑CoV‑2 Phase II–III (2,000)[122]
Multicenter, open-label, non-randomized.
Oct 2021 – Mar 2023, Japan 		Phase I–II (210)[123]
Randomized, double blind, placebo control, parallel group.[124]
Mar 2021 – Dec 2022, Japan
LYB001
Yantai Patronus Biotech Co., Ltd[125] 		China Virus-like particle[126] Phase II–III (1,900)[127]
Phase II: Randomized, double blinded, placebo-controlled
Phase III: Single-armed, open-label expanded.
Jan 2022 – Mar 2023, Laos 		Phase I (100)[128]
Randomized, double blinded, placebo-controlled.
Dec 2021 – Feb 2022, Laos
AKS-452
Akston Biosciences, University Medical Center Groningen 		Netherlands Subunit Phase II–III (1,600)[129]
Randomized, double-blinded, placebo-controlled, parallel-group, multi-centre, adaptive, seamless bridging.
Oct 2021–Dec 2022, India 		Phase I–II (112)[130]
Non-randomized, Single-center, open-label, combinatorial.
Apr–Sep 2021, Netherlands
AG0302-COVID‑19[131][132]
AnGes Inc.,[133] AMED 		Japan DNA vaccine (plasmid) Phase II–III (500)
Randomized, double-blind, placebo controlled[134]
Nov 2020 – Apr 2021, Japan 		Phase I–II (30)
Randomized/non-randomized, single-center, two doses
Jun–Nov 2020, Osaka
202-CoV
Shanghai Zerun Biotechnology Co., Ltd., Walvax Biotech 		China Subunit (Spike protein (CHO cell) 202-CoV with CpG / alum adjuvant) Phase II (1,056)[135]
Randomized, Double-blinded, Placebo-controlled.
July–Dec 2021, China 		Phase I (144)[136]
Randomized, double-blinded, placebo-controlled.
July–Dec 2021, China
Vaxart COVID-19 vaccine
Vaxart 		United States Viral vector Phase II (896)[137]
Double-Blind, Multi-Center, Randomized, Placebo-Controlled, Dose-Ranging.
Oct 2021 – Mar 2022, United States 		Phase I (83)[138][139]
Phase Ia (35): Double-blind, randomized, placebo-controlled, first-in-Human.
Phase Ib (48): Multicenter, randomized, double-blind, placebo-controlled.
Sep 2020 – Aug 2021, United States
PTX-COVID19-B[140]
Providence Therapeutics 		Canada RNA Phase II (890)[141]
Randomized, double-dummy, observer-blind.
Aug 2021–Feb 2022, Canada 		Phase I (60)[140]
First-in-Human, Observer-Blinded, Randomized, Placebo Controlled.[142]
Jan–May 2021, Canada
Unnamed
Ningbo Rong’an Biological Pharmaceutical Co., Ltd. 		China Inactivated SARS‑CoV‑2 Phase II (600)[143]
Randomized, double-blind, placebo-controlled.
Oct 2021 – Mar 2022, China 		Phase I (150)[144]
Randomized, double-blind, placebo-controlled.
Aug – Oct 2021, China
Unnamed
Tsinghua University, Tianjin Medical University,[145] Walvax Biotech 		China Viral vector Phase II (360)[146]
Jul–Nov 2021, China 		Phase I (60)[147]
May–Jun 2021, China
INNA-051
Ena Respiratory 		Australia Viral vector Phase II (423)[148]
Randomized, double-blind, placebo-controlled.
Mar  – Dec 2022, Australia 		Phase I (124)[149]
Randomised, double blind, placebo-controlled.
Jun – Oct 2021, Australia
mRNA-1283
Moderna 		United States RNA Phase II (420)[150]
Randomized, stratified, observer-blind.
Dec 2021 – Jan 2023, United States 		Phase I (106)[151]
Randomized, observer-blind, dose-ranging study.
Mar 2021 – Apr 2022, United States
Unnamed
Ihsan Gursel, Scientific and Technological Research Council of Turkey 		Turkey Virus-like particle Phase II (330)[152]
Randomized, parallel dose assigned, double blind, multi center.
Jun – Sep 2021, Turkey 		Phase I (36)[153]
double-blinded, randomised, placebo controlled.
Mar – May 2021, Turkey
COH04S1
GeoVax, City of Hope Medical Center 		United States Viral vector Phase II (240)[154]
Multi-center, observer-blinded, EUA vaccine-controlled, randomized.
Aug 2021 – Jun 2023, California 		Phase I (129)[155]
Dose Escalation Study.
Dec 2020 – Nov 2022, California
ABNCoV2
Bavarian Nordic.[156] Radboud University Nijmegen 		Denmark, Netherlands Virus-like particle Phase II (210)[157][158]
Single center, sequential dose-escalation, open labelled trial.
Aug–Dec 2021, Germany 		Phase I (42)[159]
Single center, sequential dose-escalation, open labelled trial.
Mar–Dec 2021, Netherlands
SCB-2020S
Clover Biopharmaceuticals[160] 		China Subunit Phase I–II (150)[161]
Randomized, controlled, observer-blind.
Aug 2021 – Apr 2022, Australia 		Preclinical
SCTV01C
Sinocelltech 		China Subunit Phase I–II (1,712)[162][163][164]
540+420+752=1,712: multicenter, randomized, double-blinded trial.
Aug 2021 – Jun 2023, China 		Preclinical
NDV-HXP-S (ButanVac, COVIVAC, HXP-GPOVac, Patria)
Icahn School of Medicine at Mount Sinai, Institute of Vaccines and Medical Biologicals,[165] Butantan Institute, Laboratorio Avimex, National Council of Science and Technology, Mahidol University, University of Texas at Austin 		Brazil, Mexico, Thailand, United States, Vietnam Newcastle disease virus (NDV) vector (expressing the spike protein of SARS-CoV-2, with or without the adjuvant CpG 1018)/Inactivated SARS‑CoV‑2 Phase I–II (12,750)
Randomized, placebo-controlled, observer-blind.
Mar 2021 – May 2022; Brazil (5,394), Mexico (Phase I: 90, Phase II: 396),[166] Thailand (460),[167] United States (Phase I: 35),[168] Vietnam (495)[169][170] 		Preclinical
Stemirna COVID-19 vaccine
Stemirna Therapeutics Co. Ltd. 		China RNA Phase I–II (880)[171][172]
Phase I (240): Randomized, double-blind, placebo-controlled.
Phase I/II (640): Open-label.
Mar 2021–Feb 2022, China (phase I), Lao (phase I/II) 		Preclinical
ARCT-021[173][174]
Arcturus Therapeutics, Duke–NUS Medical School 		United States, Singapore RNA Phase I–II (798)
Phase I/II (92): Randomized, double-blinded, placebo controlled
Phase II (600): Randomized, observer-blind, placebo-controlled, multiregional, multicenter trial in healthy adults to evaluate the safety, reactogenicity, and immunogenicity.[175]
Phase IIa (106): Open label extension trial to assess the safety and long-term immunogenicity by giving single-dose vaccine to the participants from the parent study that received placebo or were seronegative at screening.[176]
Aug 2020 – Apr 2022, Singapore, United States (phase IIa) 		Preclinical
Unnamed
PT Bio Farma 		Indonesia Subunit Phase I–II (780)[177]
Observer-Blind, Randomized, Controlled.
Oct 2021 – Jan 2022, Indonesia 		Preclinical
VBI-2902[178]
Variation Biotechnologies 		United States Virus-like particle Phase I (141)[179]
Randomized, observer-blind, dose-escalation, placebo-controlled
Mar 2021 – Nov 2022, Canada 		Preclinical
ICC Vaccine[180]
Novavax 		United States Subunit Phase I–II (640)[181]
Randomized, observer-blinded.
Sep 2021 – Mar 2022, Australia 		Preclinical
EuCorVac-19[182]
EuBiologics Co 		South Korea Subunit (spike protein using the recombinant protein technology and with an adjuvant) Phase I–II (280)
Dose-exploration, randomized, observer-blind, placebo-controlled
Feb 2021 – Mar 2022, the Philippines (phase II), South Korea (phase I/II) 		Preclinical
PHH-1V
Hipra[183] 		Spain Subunit Phase I–II (286)[184][185]
Phase I/IIa (30): Randomized, controlled, observer-blinded, dose-escalation.
Phase IIb (256): Randomized, controlled, observer-blinded.
Aug–Dec 2021, Spain (phase I/IIa), Vietnam (phase IIb) 		Preclinical
RBD SARS-CoV-2 HBsAg VLP
SpyBiotech 		United Kingdom Virus-like particle Phase I–II (280)[186]
Randomized, placebo-controlled, multi-center.
Aug 2020 – ?, Australia 		Preclinical
AV-COVID-19
AIVITA Biomedical, Inc., Ministry of Health (Indonesia) 		United States, Indonesia Dendritic cell vaccine (autologous dendritic cells previously loaded ex vivo with SARS-CoV-2 spike protein, with or without GM-CSF) Phase I–II (202)[187][188]
Adaptive.
Dec 2020 – Feb 2022, Indonesia (phase I), United States (phase I/II) 		Preclinical
COVID-eVax
Takis Biotech 		Italy DNA Phase I–II (160)[189]
Multicenter, open label.
Phase I: First-in-human, dose escalation.
Phase II: single arm or two arms, randomized, dose expansion.
Feb–Sep 2021, Italy 		Preclinical
BBV154[190]
Bharat Biotech[191] 		India Adenovirus vector (intranasal) Phase I–II (375)[190][192]
Phase I (175): Randomized, double-blinded, multicenter.
Phase II (200): Randomized, double blind, multicenter.[193]
Mar 2021–?, India 		Preclinical
VB10.2129 and VB10.2210
Nykode Therapeutics[194][195] 		Norway DNA Phase I–II (160)[196][197]
Open Label, Dose Escalation.
Oct 2021–Jun 2022, Norway 		Preclinical
ChulaCov19
Chulalongkorn University 		Thailand RNA Phase I–II (72)[198]
Phase 1 (72): single-center, dose-escalation, first in human study in 2 age groups: 18-55 years-old and 56-75 years-old.
Phase 2: Multi-center, observer-blinded, placebo-controlled study to assess the safety, reactogenicity, and immunogenicity in healthy adults between 18-75 years old.
May-September 2021, Thailand 		Preclinical
COVID‑19/aAPC[199]
Shenzhen Genoimmune Medical Institute[200] 		China Lentiviral vector (with minigene modifying aAPCs) Phase I (100)[199]
Single group, open-label study to evaluate safety and immunity.
Feb 2020 – Jul 2023, Shenzhen 		Preclinical
LV-SMENP-DC[201]
Shenzhen Genoimmune Medical Institute[200] 		China Lentiviral vector (with minigene modifying DCs) Phase I–II (100)[201]
Single-group, open label, multi-center study to evaluate safety and efficacy.
Mar 2020 – Jul 2023, Shenzhen 		Preclinical
ImmunityBio COVID-19 vaccine (hAd5)
ImmunityBio 		United States Viral vector Phase I–II (540)[202][203][204][205][206]
Phase 1/2 Study of the Safety, Reactogenicity, and Immunogenicity of a Subcutaneously- and Orally- Administered Supplemental Spike & Nucleocapsid-targeted COVID-19 Vaccine to Enhance T Cell Based Immunogenicity in Participants Who Have Already Received Prime + Boost Vaccines Authorized For Emergency Use.
Oct 2020  – Sep 2021, South Africa, United States 		Preclinical
COVAC[207]
VIDO (University of Saskatchewan) 		Canada Subunit (spike protein + SWE adjuvant) Phase I (120)[207]
Randomized, observer-blind, dose-escalation.[208][209]
Feb 2021 – Apr 2023, Brazil Halifax 		Preclinical
COVI-VAC (CDX-005)[210]
Codagenix Inc. 		United States Attenuated Phase I (48)[211]
First-in-human, randomised, double-blind, placebo-controlled, dose-escalation
Dec 2020 – Jun 2021, United Kingdom 		Preclinical
CoV2 SAM (LNP)
GSK 		United Kingdom RNA Phase I (40)[212]
Open-label, dose escalation, non-randomized
Feb–Jun 2021, United States 		Preclinical
COVIGEN[213]
Bionet Asia, Technovalia, University of Sydney 		Australia, Thailand DNA Phase I (150)[214]
Double-blind, dose-ranging, randomised, placebo-controlled.
Feb 2021 – Jun 2022, Australia, Thailand 		Preclinical
MV-014-212[215]
Meissa Vaccine Inc. 		United States Attenuated Phase I (130)[216]
Randomized, double-blinded, multicenter.
Mar 2021 – Oct 2022, United States 		Preclinical
KBP-201
Kentucky Bioprocessing 		United States Subunit Phase I–II (180)[217]
First-in-human, observer-blinded, randomized, placebo-controlled, parallel group
Dec 2020 – May 2022, United States 		Preclinical
AdCLD-CoV19
Cellid Co 		South Korea Viral vector Phase I–II (150)[218]
Phase I: Dose Escalation, Single Center, Open.
Phase IIa: Multicenter, Randomized, Open.
Dec 2020 – Jul 2021, South Korea 		Preclinical
AdimrSC-2f
Adimmune Corporation 		Taiwan Subunit (Recombinant RBD +/− Aluminium) Phase I–II (310)[219][220]
Phase I (70): Randomized, single center, open-label, dose-finding.
Phase I/II (240): Placebo-controlled, randomized, double-blind, dose-finding.
Aug 2020–Sep 2022, Indonesia (phase I/II), Taiwan (phase I) 		Preclinical
GLS-5310
GeneOne Life Science Inc. 		South Korea DNA Phase I–II (345)[221]
Multicenter, Randomized, Combined Phase I Dose-escalation and Phase IIa Double-blind.
Dec 2020 – Jul 2022, South Korea 		Preclinical
Covigenix VAX-001
Entos Pharmaceuticals Inc. 		Canada DNA Phase I–II (72)[222]
Placebo-controlled, randomized, observer-blind, dose ranging adaptive.
Mar–Aug 2021, Canada 		Preclinical
NBP2001
SK Bioscience Co. Ltd. 		South Korea Subunit (Recombinant protein with adjuvanted with alum) Phase I (50)[223]
Placebo-controlled, Randomized, Observer-blinded, Dose-escalation.
Dec 2020 – Apr 2021, South Korea 		Preclinical
CoVAC-1
University of Tübingen 		Germany Subunit (Peptide) Phase I–II (104)[224][225]
Phase I (36): Placebo-controlled, Randomized, Observer-blinded, Dose-escalation.
Phase I/II (68): B-pVAC-SARS-CoV-2: Phase I/II Multicenter Safety and Immunogenicity Trial of Multi-peptide Vaccination to Prevent COVID-19 Infection in Adults With Bcell/ Antibody Deficiency.
Nov 2020 – Feb 2022, Germany 		Preclinical
bacTRL-Spike
Symvivo 		Canada DNA Phase I (24)[226]
Randomized, observer-blind, placebo-controlled.
Nov 2020 – Feb 2022, Australia 		Preclinical
ChAdV68-S (SAM-LNP-S)
NIAID, Gritstone Oncology 		United States Viral vector Phase I (150)[227]
Open-label, dose and age escalation, parallel design.
Mar 2021 – Sep 2022, United States 		Preclinical
SpFN COVID-19 vaccine
WRAIR's Emerging Infectious Diseases Branch (EIDB) 		United States Subunit Phase I (72)[228]
Randomized, double-blind, placebo-controlled.
Apr 2021 – Oct 2022, United States 		Preclinical
MVA-SARS-2-S (MVA-SARS-2-ST)
University Medical Center Hamburg-Eppendorf 		Germany Viral vector Phase I–II (270)[229][230]
Phase I (30): Open, Single-center.
Phase Ib/IIa (240): Multi-center, Randomized Controlled.
Oct 2020 – Mar 2022, Germany 		Preclinical
Koçak-19 Inaktif Adjuvanlı COVID-19 vaccine
Kocak Farma 		Turkey Inactivated SARS‑CoV‑2 Phase I (38)[231]
Phase 1 Study for the Determination of Safety and Immunogenicity of Different Strengths of Koçak-19 Inaktif Adjuvanlı COVID-19 Vaccine, Given Twice Intramuscularly to Healthy Volunteers, in a Placebo Controlled Study Design.
Mar–Jun 2021, Turkey 		Preclinical
CoV2-OGEN1
Syneos Health, US Specialty Formulations 		United States Subunit Phase I (45)[232]
First-In-Human
Jun–Dec 2021, New Zealand 		Preclinical
CoVepiT
OSE Immunotherapeutics 		France Subunit Phase I (48)[233][234]
Randomized, open label.
Apr–Sept 2021, France 		Preclinical
HDT-301[235] (QTP104)
HDT Biotech Corporation, Senai Cimatec, Quartis[236] 		Brazil, South Korea, United States RNA Phase I (189)[237][238]
Phase I (90+63+36): Randomized, open-label, dose-escalation.
Aug 2021–Jul 2023, Brazil, South Korea, United States 		Preclinical
SC-Ad6-1
Tetherex Pharmaceuticals 		United States Viral vector Phase I (40)[239]
First-In-Human, Open-label, Single Ascending Dose and Multidose.
Jun–Dec 2021, Australia 		Preclinical
Unnamed
Osman ERGANIS, Scientific and Technological Research Council of Turkey 		Turkey Inactivated SARS‑CoV‑2 Phase I (50)[240]
Phase I Study Evaluating the Safety and Efficacy of the Protective Adjuvanted Inactivated Vaccine Developed Against SARS-CoV-2 in Healthy Participants, Administered as Two Injections Subcutaneously in Two Different Dosages.
Apr–Oct 2021, Turkey 		Preclinical
EXG-5003
Elixirgen Therapeutics, Fujita Health University 		Japan, United States RNA Phase I–II (60)[241]
First in Human, randomized, placebo-controlled.
Apr 2021 – Jan 2023, Japan 		Preclinical
IVX-411
Icosavax, Seqirus Inc. 		United States Virus-like particle Phase I–II (168)[242][243]
Phase I/II (84): Randomized, observer-blinded, placebo-controlled.
Jun 2021–2022, Australia 		Preclinical
QazCoVac-P[244]
Research Institute for Biological Safety Problems 		Kazakhstan Subunit Phase I–II (244)[245]
Phase I: Randomized, blind, placebo-controlled.
Phase II: Randomized, open phase.
Jun – Dec 2021, Kazakhstan 		Preclinical
LNP-nCOV saRNA-02
MRC/UVRI & LSHTM Uganda Research Unit 		Uganda RNA Phase I (42)[246]
A Clinical Trial to Assess the Safety and Immunogenicity of LNP-nCOV saRNA-02, a Self-amplifying Ribonucleic Acid (saRNA) Vaccine, in SARS-CoV-2 Seronegative and Seropositive Uganda Population.
Sep 2021 – Jun 2022, Uganda 		Preclinical
Baiya SARS-CoV-2 Vax 1[247]
Baiya Phytopharm Co Ltd. 		Thailand Plant-based Subunit (RBD-Fc + adjuvant) Phase I (96)[248]
Randomized, open-label, dose-finding.
Sep–Dec 2021, Thailand 		Preclinical
CVXGA1
CyanVac LLC 		United States Viral vector Phase I (80)[249]
Open-label
July–Dec 2021, United States 		Preclinical
Unnamed
St. Petersburg Scientific Research Institute of Vaccines and Sera of Russia at the Federal Medical Biological Agency 		Russia Subunit (Recombinant) Phase I–II (200)[250][251]
Jul–Aug 2021, Russia 		Preclinical
LVRNA009
Liverna Therapeutics Inc. 		China RNA Phase I (24)[252]
July–Nov 2021, China 		Preclinical
ARCT-165
Arcturus Therapeutics 		United States RNA Phase I–II (72)[253]
Randomized, observer-blind.
Aug 2021–Mar 2023, Singapore, United States 		Preclinical
BCD-250
Biocad 		Russia Viral vector Phase I–II (160)[254]
Randomized, double-blind, placebo-controlled, adaptive, seamless phase I/II.
Aug 2021–Aug 2022, Russia 		Preclinical
COVID-19-EDV
EnGeneIC 		Australia Viral vector Phase I (18)[255]
Open label, non-randomised, dose escalation.
Aug 2021–Jan 2022, Australia 		Preclinical
COVIDITY
Scancell 		United Kingdom DNA[256] Phase I (40)[257]
Open-label, two-arm.
Sep 2021–Apr 2022, South Africa 		Preclinical
SII Vaccine
Novavax 		United States Subunit Phase I–II (240)[258]
randomized, observer-blinded, open-label.
Oct–Nov 2021, Australia 		Preclinical
EG-COVID
Eyegene 		South Korea mRNA Phase I–II (120)[259][260][261]
Phase I/IIa: Multi-center, Open-label.
Feb 2022–May 2023, South Korea 		Preclinical
PIKA COVID-19 vaccine
Yisheng Biopharma 		China Subunit Phase I (45)[262]
Open-label, dose-escalation.
Sep–Nov 2021, New Zealand 		Preclinical
Ad5-triCoV/Mac
McMaster University, Canadian Institutes of Health Research (CIHR) 		Canada Viral vector Phase I (30)[263]
Open-label.
Nov 2021–Jun 2023, Canada 		Preclinical
Unnamed
University of Hong Kong, Immuno Cure 3 Limited 		Hong Kong DNA Phase I (30)[264]
Randomized, double-blinded, placebo-controlled, dose-escalation.
Nov 2021–Jun 2022, Hong Kong 		Preclinical
MigVax-101
Oravax Medical[265][266][267] 		Israel Virus-like particle Phase I
Oct 2021–?, South Africa 		Preclinical
IN-B009
HK inno.N[268] 		South Korea Subunit (Recombinant protein) Phase I (40)[269]
Open-label, dose-escalation.
Sep 2021–Feb 2023, South Korea 		Preclinical
naNO-COVID
Emergex Vaccines 		United Kingdom Subunit Phase I (26)[270]
Double-blind, randomized, vehicle-controlled, dose-finding.
Nov 2021–Sep 2022, Switzerland 		Preclinical
Betuvax-CoV-2
Human Stem Cells Institute 		Russia Subunit Phase I–II (170)[271][272]
Sep 2021–?, Russia 		Preclinical
Covi Vax[273]
National Research Centre 		Egypt Inactivated SARS‑CoV‑2 Phase I (72)[274]
Randomized, open-labeled
Nov 2021–Feb 2023, Egypt 		Preclinical
VLPCOV-01
VLP Therapeutics 		United States mRNA Phase I (45)[275]
Randomized, placebo-controlled, parallel group, first-in-human.
Aug 2021–Jan 2023, Japan 		Preclinical
GRT-R910
Gritstone Oncology 		United States mRNA Phase I (120)[276]
A Phase 1 Trial to Evaluate the Safety, Immunogenicity, and Reactogenicity of a Self-Amplifying mRNA Prophylactic Vaccine Boost Against SARS-CoV-2 in Previously Vaccinated Healthy Elderly Adults.
Sep 2021–Nov 2022, United Kingdom 		Preclinical
Unnamed
DreamTec Limited 		Hong Kong Subunit Phase I (30)[277]
Development of a COVID19 Oral Vaccine Consisting of Bacillus Subtilis Spores Expressing and Displaying the Receptor Binding Domain of Spike Protein of SARS-COV2.
Apr–Dec 2021, Hong Kong 		Preclinical
Almansour-001
Imam Abdulrahman Bin Faisal University, ICON plc 		Ireland, Saudi Arabia DNA Phase I (30)[278]
Single center, randomized, observer blind, dosage finding.
Feb–Jul 2022, Ireland, Saudi Arabia 		Preclinical
Unnamed
North's Academy of Medical Science Medical biology institute 		North Korea Subunit (spike protein with Angiotensin-converting enzyme 2) Phase I–II (?)[279]
Jul 2020, North Korea 		Preclinical
Vabiotech COVID-19 vaccine
Vaccine and Biological Production Company No. 1 (Vabiotech) 		Vietnam Subunit Preclinical
Awaited for the conduct on Phase I trial.[280] 		?
INO-4802
Inovio 		United States DNA Preclinical
Awaited for the conduct on Phase I/II trials.[281] 		?
Bangavax (Bancovid)[282][283]
Globe Biotech Ltd. of Bangladesh 		Bangladesh RNA Preclinical
Awaiting for approval from Bangladesh government to conduct the first clinical trial.[284] 		?
Unnamed
Indian Immunologicals, Griffith University[285] 		Australia, India Attenuated Preclinical ?
EPV-CoV-19[286]
EpiVax 		United States Subunit (T cell epitope-based protein) Preclinical ?
Unnamed
Intravacc[287] 		Netherlands Subunit Preclinical ?
CureVac–GSK COVID-19 vaccine[288]
CureVac, GSK 		Germany, United Kingdom RNA Preclinical ?
DYAI-100[289] Sorrento Therapeutics, Dyadic International, Inc.[290] United States Subunit Preclinical ?
Unnamed[291]
Ministry of Health (Malaysia), Malaysia Institute of Medical Research Malaysia, Universiti Putra Malaysia 		Malaysia RNA Preclinical ?
CureVac COVID-19 vaccine (CVnCoV)
CureVac, CEPI 		Germany RNA (unmodified RNA)[292] Terminated (44,433)[293][294][295][296][297]
Phase 2b/3 (39,693): Multicenter efficacy and safety trial in adults.
Phase 3 (2,360+180+1,200+1,000=4,740): Randomized, placebo-controlled, multicenter, some observer-blinded, some open-labeled.
Nov 2020 – Jun 2022, Argentina, Belgium, Colombia, Dominican Republic, France, Germany, Mexico, Netherlands, Panama, Peru, Spain[298] 		Phase I–II (944)[299][300]
Phase I (284): Partially blind, controlled, dose-escalation to evaluate safety, reactogenicity and immunogenicity.
Phase IIa (660):Partially observer-blind, multicenter, controlled, dose-confirmation.
Jun 2020 – Oct 2021, Belgium (phase I), Germany (phase I), Panama (phase IIa), Peru (phase IIa)
Emergency (2)
CORVax12
OncoSec Medical, Providence Health & Services 		United States DNA Terminated (36)[303]
Open-label, non-randomized, parallel assignment study to evaluate the safety of prime & boost doses with/without the combination of electroporated IL-12p70 plasmid in 2 age groups: 18-50 years-old and > 50 years-old.
Dec 2020 – Jul 2021, United States 		Preclinical
Sanofi–Translate Bio COVID-19 vaccine (MRT5500)[304]
Sanofi Pasteur and Translate Bio 		France, United States RNA Terminated (415)[305]
Interventional, randomized, parallel-group, sequential study consisting of a sentinel cohort followed by the full enrollment cohort. The sentinel cohort is an open-label, step-wise, dose-ranging study to evaluate the safety of 3 dose levels with 2 vaccinations. The full enrollment cohort is a quadruple-blinded study of safety and immunogenicity in 2 age groups, with half receiving a single injection, and the other half receiving 2 injections.
Mar 2021 – Sep 2021, Honduras, United States, Australia 		Preclinical
AdCOVID
Altimmune Inc. 		United States Viral vector Terminated (180)[306][307]
Double-blind, randomized, placebo-controlled, first-in-Human.
Feb 2021 – Feb 2022, United States 		Preclinical
LNP-nCoVsaRNA[308]
MRC clinical trials unit at Imperial College London 		United Kingdom RNA Terminated (105)
Randomized trial, with dose escalation study (15) and expanded safety study (at least 200)
Jun 2020 – Jul 2021, United Kingdom 		?
TMV-083
Institut Pasteur 		France Viral vector Terminated (90)[309]
Randomized, Placebo-controlled.
Aug 2020 – Jun 2021, Belgium, France 		?
SARS-CoV-2 Sclamp/V451[310][311][unreliable source?]
UQ, Syneos Health, CEPI, Seqirus 		Australia Subunit (molecular clamp stabilized spike protein with MF59) Terminated (120)
Randomised, double-blind, placebo-controlled, dose-ranging.
False positive HIV test found among participants.
Jul–Oct 2020, Brisbane 		?
V590[312] and V591/MV-SARS-CoV-2[313] Merck & Co. (Themis BIOscience), Institut Pasteur, University of Pittsburgh's Center for Vaccine Research (CVR), CEPI United States, France Vesicular stomatitis virus vector[314] / Measles virus vector[315][unreliable source?] Terminated
In phase I, immune responses were inferior to those seen following natural infection and those reported for other SARS-CoV-2/COVID-19 vaccines.[316]
  1. ^ Latest Phase with published results.
  2. ^ Phase I–IIa in South Korea in parallel with Phase II–III in the US


Homologous prime-boost vaccination

In July 2021, the U.S. Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) issued a joint statement reporting that a booster dose is not necessary for those who have been fully vaccinated.[317]

In August 2021, the FDA and the CDC authorized the use of an additional mRNA vaccine dose for immunocompromised individuals.[318][319] The authorization was extended to cover other specific groups in September 2021.[320][321][322]

In October 2021, the FDA and the CDC authorized the use of either homologous or heterologous vaccine booster doses.[323][324]

Heterologous prime-boost vaccination

The World Health Organization (WHO) defines heterologous prime-boost immunization as the "administration of two different vectors or delivery systems expressing the same or overlapping antigenic inserts."[325] A heterologous scheme can sometimes be more immunogenic than some homologous schemes.[326]

In October 2021, the FDA and the CDC authorized the use of either homologous or heterologous vaccine booster doses.[323][324]

Some experts believe that heterologous prime-boost vaccination courses can boost immunity, and several studies have begun to examine this effect.[327] Despite the absence of clinical data on the efficacy and safety of such heterologous combinations, Canada and several European countries have recommended a heterologous second dose for people who have received the first dose of the Oxford–AstraZeneca vaccine.[328]

In February 2021, the Oxford Vaccine Group launched the Com-COV vaccine trial to investigate heterologous prime-boost courses of different COVID-19 vaccines.[329] As of June 2021, the group is conducting two phase II studies: Com-COV and Com-COV2.[330]

In Com-COV, the two heterologous combinations of the Oxford–AstraZeneca and Pfizer–BioNTech vaccines were compared with the two homologous combinations of the same vaccines, with an interval of 28 or 84 days between doses.[331][332][unreliable medical source?]

In Com-COV2, the first dose is the Oxford–AstraZeneca vaccine or the Pfizer vaccine, and the second dose is the Moderna vaccine, the Novavax vaccine, or a homologous vaccine equal to the first dose, with an interval of 56 or 84 days between doses.[333]

A study in the UK is evaluating annual heterologous boosters by randomly combining the following vaccines: Oxford–AstraZeneca, Pfizer–BioNTech, Moderna, Novavax, VLA2001, CureVac, and Janssen.[334]

On 16 December, WHO recommendations on heterologous vaccinations suggested a general trend of increased immunogenicity when one of the doses is of an mRNA vaccine, particularly as the last dose. The immunogenicity of a homologous mRNA course is roughly equivalent to a heterologous scheme involving a vector vaccine and an mRNA vaccine. However, the WHO has emphasized the need to address many evidence gaps in heterologous regimens, including duration of protection, optimal interval between doses, influence of fractional dosing, effectiveness against variants and long-term safety.[335]

Heterologous second dose regimes in clinical trial
First dose Second dose Schedules Current phase (participants), periods and locations
Oxford–AstraZeneca
Pfizer–BioNTech 		Oxford–AstraZeneca
Pfizer–BioNTech 		Days 0 and 28
Days 0 and 84 		Phase II (820)[331]
Feb–Aug 2021, United Kingdom
Sputnik Light Oxford–AstraZeneca
Moderna
Sinopharm BIBP 		Phase II (121)[336]
Feb–Aug 2021, Argentina
Oxford–AstraZeneca
Pfizer–BioNTech 		Oxford–AstraZeneca
Pfizer–BioNTech
Moderna
Novavax 		Days 0 and 56–84 Phase II (1,050)[333]
Mar 2021 – Sep 2022, United Kingdom
Convidecia ZF2001 Days 0 and 28
Days 0 and 56 		Phase IV (120)[337]
Apr–Dec 2021, China
Oxford–AstraZeneca Pfizer–BioNTech Days 0 and 28 Phase II (676)[338]
Apr 2021 – Apr 2022, Spain
Oxford–AstraZeneca
Pfizer–BioNTech
Moderna 		Pfizer–BioNTech
Moderna 		Days 0 and 28
Days 0 and 112 		Phase II (1,200)[339]
May 2021 – Mar 2023, Canada
Pfizer–BioNTech
Moderna 		Pfizer–BioNTech
Moderna 		Days 0 and 42 Phase II (400)[340]
May 2021 – Jan 2022, France
Oxford–AstraZeneca Pfizer–BioNTech Days 0 and 28
Days 0 and 21–49 		Phase II (3,000)[341]
May–Dec 2021, Austria
Janssen Pfizer–BioNTech
Janssen
Moderna 		Days 0 and 84 Phase II (432)[342]
Jun 2021 – Sep 2022, Netherlands
Heterologous booster dose regimes in clinical trial
Initial course Booster dose Interval Current phase (participants), periods and locations
CoronaVac (2 doses) CoronaVac
Pfizer–BioNTech
Oxford–AstraZeneca 		19 weeks or more Phase IV (2,017,878)[343][344]
Aug–Nov 2021, Chile

Efficacy

 
Cumulative incidence curves for symptomatic COVID-19 infections after the first dose of the Pfizer–BioNTech vaccine (tozinameran) or placebo in a double-blind clinical trial (red: placebo; blue: tozinameran)[345]

Vaccine efficacy is the reduction in risk of getting the disease by vaccinated participants in a controlled trial compared with the risk of getting the disease by unvaccinated participants.[346] An efficacy of 0% means that the vaccine does not work (identical to placebo). An efficacy of 50% means that there are half as many cases of infection as in unvaccinated individuals.[citation needed]

COVID-19 vaccine efficacy may be adversely affected if the arm is held improperly or squeezed so the vaccine is injected subcutaneously instead of into the muscle.[347][348] The CDC guidance is to not repeat doses that are administered subcutaneously.[349]

It is not straightforward to compare the efficacies of the different vaccines because the trials were run with different populations, geographies, and variants of the virus.[350] In the case of COVID-19 prior to the advent of the delta variant, it was thought that a vaccine efficacy of 67% may be enough to slow the pandemic, but the current vaccines do not confer sterilizing immunity,[351] which is necessary to prevent transmission. Vaccine efficacy reflects disease prevention, a poor indicator of transmissibility of SARS‑CoV‑2 since asymptomatic people can be highly infectious.[352] The US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) set a cutoff of 50% as the efficacy required to approve a COVID-19 vaccine, with the lower limit of the 95% confidence interval being greater than 30%.[353][354][355] Aiming for a realistic population vaccination coverage rate of 75%, and depending on the actual basic reproduction number, the necessary effectiveness of a COVID-19 vaccine is expected to need to be at least 70% to prevent an epidemic and at least 80% to extinguish it without further measures, such as social distancing.[356]

The observed substantial efficacy of certain mRNA vaccines even after partial (1-dose) immunization[357][345] indicates a non-linear dose-efficacy relation already seen in the phase I-II study.[358] It suggests that personalization of the vaccine dose (regular dose to the elderly, reduced dose to the healthy young,[359] additional booster dose to the immunosuppressed[360]) might allow accelerating vaccination campaigns in settings of limited supplies, thereby shortening the pandemic, as predicted by pandemic modeling.[361]

Ranges below are 95% confidence intervals unless indicated otherwise, and all values are for all participants regardless of age, according to the references for each of the trials. By definition, the accuracy of the estimates without an associated confidence interval is unknown publicly. Efficacy against severe COVID-19 is the most important, since hospitalizations and deaths are a public health burden whose prevention is a priority.[362] Authorized and approved vaccines have shown the following efficacies:

COVID-19 vaccine efficacy
(
)
Vaccine Efficacy by severity of COVID-19 Trial location Refs
Mild or moderate[A] Severe without hospitalization or death[B] Severe with hospitalization or death[C]
Oxford–AstraZeneca 81% (60–91%)[D] 100% (97.5% CI, 72–100%) 100%[E] Multinational [363]
74% (68–82%)[F] 100%[E] 100%[E] United States [364]
Pfizer–BioNTech 95% (90–98%)[G] 66% (−125 to 96%)[H][G] Multinational [365]
95% (90–98%)[G] Not reported Not reported United States [366]
Janssen 66% (55–75%)[I][J] 85% (54–97%)[J] 100%[E][J][K] Multinational [367]
72% (58–82%)[I][J] 86% (−9 to 100%)[H][J] 100%[E][J][K] United States
68% (49–81%)[I][J] 88% (8–100%)[H][J] 100%[E][J][K] Brazil
64% (41–79%)[I][J] 82% (46–95%)[J] 100%[E][J][K] South Africa
Moderna 94% (89–97%)[L] 100%[E][M] 100%[E][M] United States [369]
Sinopharm BIBP 78% (65–86%) 100%[E] 100%[E] Multinational [370]
79% (66–88%) Not reported 79% (26–94%)[H] Multinational [371]
Sputnik V 92% (86–95%) 100% (94–100%) 100%[E] Russia [372]
CoronaVac 51% (36–62%)[N] 84% (58–94%)[N] 100% (56–100%)[N] Brazil [373][374][375]
84% (65–92%) 100%[E] 100% (20–100%)[H] Turkey [376]
Covaxin 78% (65–86%) 93% (57–100%) India [377][378]
Sputnik Light 79%[E] Not reported Not reported Russia [379]
Convidecia 66%[E][N] 91%[E][N] Not reported Multinational [380][unreliable medical source?]
Sinopharm WIBP 73% (58–82%) 100%[E][O] 100%[E][O] Multinational [381]
Abdala 92% (86–96%) Not reported Not reported Cuba [382][383][unreliable medical source?]
Soberana 02 71% (59–79%) 63%[E] Not reported Cuba [384]
67% (59–79%) 97%[E] 95%[E] Iran [385][386]
Soberana 02 and Soberana Plus 92% (87–96%) 100%[E] Not reported Cuba [384]
Novavax 90% (75–95%) 100%[E][O] 100%[E][O] United Kingdom [387][388][389]
60% (20–80%)[H] 100%[E][O] 100%[E][O] South Africa
90% (83–95%) Not reported Not reported United States
Not reported Not reported Mexico
CureVac 48%[E] Not reported Not reported Multinational [390]
ZyCoV-D 67%[E] Not reported Not reported India [391][unreliable medical source?]
EpiVacCorona 79%[E] Not reported Not reported Russia [392][unreliable medical source?]
ZF2001 82%[E] Not reported Not reported Multinational [393][unreliable medical source?]
SCB-2019 67% (54–77%) Not reported Not reported Multinational [394]
CoVLP 71% (59–80%) Not reported Not reported Multinational [395]
Sanofi–GSK COVID-19 vaccine 58% (27–77%) Not reported Not reported Multinational [396]
  1. ^ Mild symptoms: fever, dry cough, fatigue, myalgia, arthralgia, sore throat, diarrhea, nausea, vomiting, headache, anosmia, ageusia, nasal congestion, rhinorrhea, conjunctivitis, skin rash, chills, dizziness. Moderate symptoms: mild pneumonia.
  2. ^ Severe symptoms without hospitalization or death for an individual, are any one of the following severe respiratory symptoms measured at rest on any time during the course of observation (on top of having either pneumonia, deep vein thrombosis, dyspnea, hypoxia, persistent chest pain, anorexia, confusion, fever above 38 °C (100 °F)), that however were not persistent/severe enough to cause hospitalization or death: Any respiratory rate ≥30 breaths/minute, heart rate ≥125 beats/minute, oxygen saturation (SpO2) ≤93% on room air at sea level, or partial pressure of oxygen/fraction of inspired oxygen (PaO2/FiO2) <300 mmHg.
  3. ^ Severe symptoms causing hospitalization or death, are those requiring treatment at hospitals or results in deaths: dyspnea, hypoxia, persistent chest pain, anorexia, confusion, fever above 38 °C (100 °F), respiratory failure, kidney failure, multiorgan dysfunction, sepsis, shock.
  4. ^ With twelve weeks or more between doses. For an interval of less than six weeks, the trial found an efficacy 55% (33–70%).
  5. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad A confidence interval was not provided, so it is not possible to know the accuracy of this measurement.
  6. ^ With a four-week interval between doses. Efficacy is "at preventing symptomatic COVID-19".
  7. ^ a b c COVID-19 symptoms observed in the Pfizer–BioNTech vaccine trials, were only counted as such for vaccinated individuals if they began more than seven days after their second dose, and required presence of a positive RT-PCR test result. Mild/moderate cases required at least one of the following symptoms and a positive test during, or within 4 days before or after, the symptomatic period: fever; new or increased cough; new or increased shortness of breath; chills; new or increased muscle pain; new loss of taste or smell; sore throat; diarrhoea; or vomiting. Severe cases additionally required at least one of the following symptoms: clinical signs at rest indicative of severe systemic illness (RR ≥30 breaths per minute, HR ≥125 beats per minute, SpO2 ≤93% on room air at sea level, or PaO2/FiO2<300mm Hg); respiratory failure (defined as needing high-flow oxygen, non-invasive ventilation, mechanical ventilation, or ECMO); evidence of shock (SBP <90 mm Hg, DBP <60 mm Hg, or requiring vasopressors); significant acute renal, hepatic, or neurologic dysfunction; admission to an ICU; death.[365][366]
  8. ^ a b c d e f This measurement is not accurate enough to support the high efficacy because the lower limit of the 95% confidence interval is lower than the minimum of 30%.
  9. ^ a b c d Moderate cases.
  10. ^ a b c d e f g h i j k l Efficacy reported 28 days post-vaccination for the Janssen single shot vaccine. A lower efficacy was found for the vaccinated individuals 14 days post-vaccination.[367]
  11. ^ a b c d No hospitalizations or deaths were detected 28 days post-vaccination for 19,630 vaccinated individuals in the trials, compared with 16 hospitalizations reported in the placebo group of 19,691 individuals (incidence rate 5.2 per 1000 person-years)[367] and seven COVID-19 related deaths for the same placebo group.[368]
  12. ^ Mild/Moderate COVID-19 symptoms observed in the Moderna vaccine trials, were only counted as such for vaccinated individuals if they began more than 14 days after their second dose, and required presence of a positive RT-PCR test result along with at least two systemic symptoms (fever above 38ºC, chills, myalgia, headache, sore throat, new olfactory and taste disorder) or just one respiratory symptom (cough, shortness of breath or difficulty breathing, or clinical or radiographical evidence of pneumonia).[369]
  13. ^ a b Severe COVID-19 symptoms observed in the Moderna vaccine trials, were defined as symptoms having met the criteria for mild/moderate symptoms plus any of the following observations: Clinical signs indicative of severe systemic illness, respiratory rate ≥30 per minute, heart rate ≥125 beats per minute, SpO2 ≤93% on room air at sea level or PaO2/FIO2 <300 mm Hg; or respiratory failure or ARDS, (defined as needing high-flow oxygen, non-invasive or mechanical ventilation, or ECMO), evidence of shock (systolic blood pressure <90 mmHg, diastolic BP <60 mmHg or requiring vasopressors); or significant acute renal, hepatic, or neurologic dysfunction; or admission to an intensive care unit or death. No severe cases were detected for vaccinated individuals in the trials, compared with thirty in the placebo group (incidence rate 9.1 per 1000 person-years).[369]
  14. ^ a b c d e These Phase III data have not been published or peer reviewed.
  15. ^ a b c d e f No cases detected in trial.


Effectiveness

See also: SARS-CoV-2 Delta variant § Prevention, and SARS-CoV-2 Omicron variant § Prevention
 
Death rates for unvaccinated Americans substantially exceed those who were vaccinated, with bivalent boosters further reducing the death rate.[397]

Evidence from vaccine use during the pandemic shows vaccination can reduce infection and is most effective at preventing severe COVID-19 symptoms and death, but is less good at preventing mild COVID-19. Efficacy wanes over time but can be maintained with boosters.[398] In 2021, the CDC reported that unvaccinated people were 10 times more likely to be hospitalized and 11 times more likely to die than fully vaccinated people.[399][400]

The CDC reported that vaccine effectiveness fell from 91% against Alpha to 66% against Delta.[401] One expert stated that "those who are infected following vaccination are still not getting sick and not dying like was happening before vaccination."[402] By late August 2021, the Delta variant accounted for 99 percent of U.S. cases and was found to double the risk of severe illness and hospitalization for those not yet vaccinated.[403]

In November 2021, a study by the ECDC estimated that 470,000 lives over the age of 60 had been saved since the start of the vaccination roll-out in the European region.[404]

On 10 December 2021, the UK Health Security Agency reported that early data indicated a 20- to 40-fold reduction in neutralizing activity for Omicron by sera from Pfizer 2-dose vaccinees relative to earlier strains. After a booster dose (usually with an mRNA vaccine),[405] vaccine effectiveness against symptomatic disease was at 70%–75%, and the effectiveness against severe disease was expected to be higher.[406]

According to early December 2021 CDC data, "unvaccinated adults were about 97 times more likely to die from COVID-19 than fully vaccinated people who had received boosters".[407]

A meta-analysis looking into COVID-19 vaccine differences in immunosuppressed individuals found that people with a weakened immune system are less able to produce neutralizing antibodies. For example, organ transplant recipients need three vaccines to achieve seroconversion.[408] A study on the serologic response to mRNA vaccines among patients with lymphoma, leukemia, and myeloma found that one-quarter of patients did not produce measurable antibodies, varying by cancer type.[409]

In February 2023, a systematic review in The Lancet said that the protection afforded by infection was comparable to that from vaccination, albeit with an increased risk of severe illness and death from the disease of an initial infection.[410]

A January 2024 study by the CDC found that staying up to date on the vaccines could reduce the risk of strokes, blood clots and heart attacks related to COVID-19 in people aged 65 years or older or with a condition that makes them more vulnerable to said conditions.[411][412]

Studies

Real-world studies of vaccine effectiveness measure the extent to which a certain vaccine prevents infection, symptoms, hospitalization and death for the vaccinated individuals in a large population under routine conditions.[413]

  • In Israel, among the 715,425 individuals vaccinated by the mRNA vaccines from 20 December 2020, to 28 January 2021, starting seven days after the second shot, only 317 people (0.04%) displayed mild/moderate COVID-19 symptoms and only 16 people (0.002%) were hospitalized.[414]
  • CDC reported that under real-world conditions, mRNA vaccine effectiveness was 90% against infections regardless of symptom status; while effectiveness of partial immunization was 80%.[415]
  • In the UK, 15,121 health care workers from 104 hospitals who had tested negative for antibodies prior to the study, were followed by RT-PCR tests twice a week from 7 December 2020 to 5 February 2021, a study compared the positive results for the 90.7% vaccinated share of their cohort with the 9.3% unvaccinated share, and found that the Pfizer-BioNTech vaccine reduced all infections (including asymptomatic), by 72% (58–86%) three weeks after the first dose and 86% (76–97%) one week after the second dose, while Alpha was dominant.[416][needs update]
  • In Israel a study conducted from 17 January to 6 March 2021, found that Pfizer/BioNTech reduced asymptomatic Alpha infections by 94% and symptomatic COVID-19 infections by 97%.[417]
  • A study on the Queensland Population having only ever been exposed to the Omicron strain of COVID-19 found vaccine effectiveness against symptomatic hospitalizations to be 70% in the general population and similar for First Nations peoples.[418]
  • A study among pre-surgical patients across the Mayo Clinic system in the United States, showed that mRNA vaccines were 80% protective against asymptomatic infections.[419]
  • A UK study found that a single dose of the Oxford–AstraZeneca COVID-19 vaccine is about 73% (27–90%) effective in people aged 70 and older.[420]
  • A study finds that nearly all teenagers admitted to intensive care units because of COVID-19 were unvaccinated.[421]

Pregnancy and fertility

Studies have not observed a correlation between COVID vaccination and fertility.[422][423]

A UK study found COVID vaccination is safe for pregnant women and is associated with a 15% decrease in the odds of stillbirth. Vaccination is recommended for pregnant women because pregnancy increases the risk of severe COVID. Researchers at St George's, University of London, and the Royal College of Obstetricians and Gynaecologists investigated 23 published studies and trials involving 117,552 vaccinated pregnant women. There was no increased risk of complications during pregnancy. Almost all pregnant women admitted to UK hospitals with COVID were unvaccinated.[424][425]

A US study of 46,079 pregnancies concluded that COVID vaccination is safe and does not raise the risk of preterm birth or small size babies.[426]

(
)
Vaccine Initial effectiveness by severity of COVID-19 Study location Refs
Asymptomatic Symptomatic Hospitalization Death
Oxford–AstraZeneca 70% (69–71%) Not reported 87% (85–88%) 90% (88–92%) Brazil [427]
Not reported 89% (78–94%)[i] Not reported Not reported England [429]
Not reported Not reported Not reported 89%[ii] Argentina [430]
72% (69–74%) Not reported Not reported 88% (79–94%) Hungary [431]
Pfizer–BioNTech 92% (91–92%) 97% (97–97%) 98% (97–98%) 97% (96–97%) Israel [432]
92% (88–95%) 94% (87–98%) 87% (55–100%) 97%[ii] Israel [433][434]
83% (83–84%) Not reported Not reported 91% (89–92%) Hungary [431]
Not reported 78% (77–79%) 98% (96–99%) 96% (95–97%) Uruguay [435]
85% (74–96%) Not reported Not reported England [436]
90% (68–97%) Not reported 100%[ii][iii] United States [437]
Moderna 89% (87–90%) Not reported Not reported 94% (91–96%) Hungary [431]
90% (68–97%) Not reported 100%[ii][iii] United States [437]
Sinopharm BIBP Not reported Not reported Not reported 84%[ii] Argentina [430]
69% (67–70%) Not reported Not reported 88% (86–89%) Hungary [431]
50% (49–52%) Not reported Not reported 94% (91–96%) Peru [438]
Sputnik V Not reported 98%[ii] Not reported Not reported Russia [439][440]
Not reported 98%[ii] 100%[ii][iii] 100%[ii][iii] United Arab Emirates [441]
Not reported Not reported Not reported 93%[ii] Argentina [430]
86% (84–87%) Not reported Not reported 98% (96–99%) Hungary [431]
CoronaVac 54% (53–55%) Not reported 73% (72–74%) 74% (73–75%) Brazil [427]
Not reported 66% (65–67%) 88% (87–88%) 86% (85–88%) Chile [442][443]
Not reported 60% (59–61%) 91% (89–93%) 95% (93–96%) Uruguay [435]
Not reported 94%[ii] 96%[ii] 98%[ii] Indonesia [444][445]
Not reported 80%[ii] 86%[ii] 95%[ii] Brazil [446][447]
Sputnik Light 79% (75–82%)[ii][iv] Not reported 88% (80–92%)[ii][iv] 85% (75–91%)[ii][iv] Argentina [448]
  1. ^ Data collected while the Alpha variant was already dominant.[428]
  2. ^ a b c d e f g h i j k l m n o p q r s A confidence interval was not provided, so it is not possible to know the accuracy of this measurement.
  3. ^ a b c d No cases detected in study.
  4. ^ a b c Participants aged 60 to 79.
(
)
Initial course Booster dose Initial effectiveness by severity of COVID-19 Study location Refs
Asymptomatic Symptomatic Hospitalization Death
CoronaVac CoronaVac Not reported 80%[I] 88%[I] Not reported Chile [449]
Pfizer–BioNTech Not reported 90%[I] 87%[I] Not reported Chile [449]
Oxford–AstraZeneca Not reported 93%[I] 96%[I] Not reported Chile [449]
  1. ^ a b c d e f A confidence interval was not provided, so it is not possible to know the accuracy of this measurement.


Variants

See also: Variants of SARS-CoV-2
World Health Organization video describing how variants proliferate in unvaccinated areas

The interplay between the SARS-CoV-2 virus and its human hosts was initially natural but is now being altered by the prompt availability of vaccines.[450] The potential emergence of a SARS-CoV-2 variant that is moderately or fully resistant to the antibody response elicited by the COVID-19 vaccines may necessitate modification of the vaccines.[451] The emergence of vaccine-resistant variants is more likely in a highly vaccinated population with uncontrolled transmission.[452] Trials indicate many vaccines developed for the initial strain have lower efficacy for some variants against symptomatic COVID-19.[453] As of February 2021, the US Food and Drug Administration believed that all FDA authorized vaccines remained effective in protecting against circulating strains of SARS-CoV-2.[451]

Alpha (lineage B.1.1.7)

Further information: SARS-CoV-2 Alpha variant

Limited evidence from various preliminary studies reviewed by the WHO indicated retained efficacy/effectiveness against disease from Alpha with the Oxford–AstraZeneca vaccine, Pfizer–BioNTech and Novavax, with no data for other vaccines yet. Relevant to how vaccines can end the pandemic by preventing asymptomatic infection, they have also indicated retained antibody neutralization against Alpha with most of the widely distributed vaccines (Sputnik V, Pfizer–BioNTech, Moderna, CoronaVac, Sinopharm BIBP, Covaxin), minimal to moderate reduction with the Oxford–AstraZeneca and no data for other vaccines yet.[454]

In December 2020, a new SARS‑CoV‑2 variant, the Alpha variant or lineage B.1.1.7, was identified in the UK.[455]

Early results suggest protection to the variant from the Pfizer-BioNTech and Moderna vaccines.[456][457]

One study indicated that the Oxford–AstraZeneca COVID-19 vaccine had an efficacy of 42–89% against Alpha, versus 71–91% against other variants.[458][unreliable medical source?]

Preliminary data from a clinical trial indicates that the Novavax vaccine is ~96% effective for symptoms against the original variant and ~86% against Alpha.[459]

Beta (lineage B.1.351)

Further information: SARS-CoV-2 Beta variant

Limited evidence from various preliminary studies reviewed by the WHO have indicated reduced efficacy/effectiveness against disease from Beta with the Oxford–AstraZeneca vaccine (possibly substantial), Novavax (moderate), Pfizer–BioNTech and Janssen (minimal), with no data for other vaccines yet. Relevant to how vaccines can end the pandemic by preventing asymptomatic infection, they have also indicated possibly reduced antibody neutralization against Beta with most of the widely distributed vaccines (Oxford–AstraZeneca, Sputnik V, Janssen, Pfizer–BioNTech, Moderna, Novavax; minimal to substantial reduction) except CoronaVac and Sinopharm BIBP (minimal to modest reduction), with no data for other vaccines yet.[454]

Moderna has launched a trial of a vaccine to tackle the Beta variant or lineage B.1.351.[460] On 17 February 2021, Pfizer announced neutralization activity was reduced by two-thirds for this variant, while stating that no claims about the efficacy of the vaccine in preventing illness for this variant could yet be made.[461] Decreased neutralizing activity of sera from patients vaccinated with the Moderna and Pfizer-BioNTech vaccines against Beta was later confirmed by several studies.[457][462] On 1 April 2021, an update on a Pfizer/BioNTech South African vaccine trial stated that the vaccine was 100% effective so far (i.e., vaccinated participants saw no cases), with six of nine infections in the placebo control group being the Beta variant.[463]

In January 2021, Johnson & Johnson, which held trials for its Janssen vaccine in South Africa, reported the level of protection against moderate to severe COVID-19 infection was 72% in the United States and 57% in South Africa.[464][465][466]

On 6 February 2021, the Financial Times reported that provisional trial data from a study undertaken by South Africa's University of the Witwatersrand in conjunction with Oxford University demonstrated reduced efficacy of the Oxford–AstraZeneca COVID-19 vaccine against the variant.[467] The study found that in a sample size of 2,000 the AZD1222 vaccine afforded only "minimal protection" in all but the most severe cases of COVID-19.[468] On 7 February 2021, the Minister for Health for South Africa suspended the planned deployment of about a million doses of the vaccine whilst they examine the data and await advice on how to proceed.[468][469]

In a study reported in March[470] and May 2021,[471] the efficacy of the Novavax vaccine (NVX-CoV2373) was tested in a preliminary randomized, placebo-controlled study involving 2684 participants who were negative for COVID at baseline testing. Beta was the predominant variant to occur, with post-hoc analysis indicating a vaccine efficacy of Novavax against Beta of 51.0% for HIV-negative participants.[6][471]

Gamma (lineage P.1)

Further information: SARS-CoV-2 Gamma variant

Limited evidence from various preliminary studies[when?] reviewed by the WHO have indicated likely retained efficacy/effectiveness against disease from Gamma with CoronaVac and Sinopharm BIBP, with no data for other vaccines yet. Relevant to how vaccines can end the pandemic by preventing asymptomatic infection, they have also indicated retained antibody neutralization against Gamma with Oxford–AstraZeneca and CoronaVac (no to minimal reduction) and slightly reduced neutralization with Pfizer–BioNTech and Moderna (minimal to moderate reduction), with no data for other vaccines yet.[454]

The Gamma variant or lineage P.1 variant (also known as 20J/501Y.V3), initially identified in Brazil, seems to partially escape vaccination with the Pfizer-BioNTech vaccine.[462]

Delta (lineage B.1.617.2)

Further information: SARS-CoV-2 Delta variant

Limited evidence from various preliminary studies[when?] reviewed by the WHO have indicated likely retained efficacy/effectiveness against disease from Delta with the Oxford–AstraZeneca vaccine and Pfizer–BioNTech, with no data for other vaccines yet. Relevant to how vaccines can end the pandemic by preventing asymptomatic infection, they have also indicated reduced antibody neutralization against Delta with single-dose Oxford–AstraZeneca (substantial reduction), Pfizer–BioNTech and Covaxin (modest to moderate reduction), with no data for other vaccines yet.[454]

In October 2020, a new variant was discovered in India, which was named lineage B.1.617. There were very few detections until January 2021, but by April it had spread to at least 20 countries in all continents except Antarctica and South America.[472][473][474] Mutations present in the spike protein in the B.1.617 lineage are associated with reduced antibody neutralization in laboratory experiments.[475][476] The variant has frequently been referred to as a 'Double mutant', even though in this respect it is not unusual.[477] the latter two of which may cause it to easily avoid antibodies.[478] In an update on 15 April 2021, PHE designated lineage B.1.617 as a 'Variant under investigation', VUI-21APR-01.[479] On 6 May 2021, Public Health England escalated lineage B.1.617.2 from a Variant Under Investigation to a Variant of Concern based on an assessment of transmissibility being at least equivalent to the Alpha variant.[480]

Omicron (lineage BA.2 and BA.2.12.2)

COVID-19 vaccine effectiveness was studied in adults without immunocompromising conditions in 10 US states between 18 December 2021 – 10 June 2022, when Omicron was prevalent. 3 doses of mRNA COVID-19 vaccines was 69% against COVID-19–associated hospitalization 7–119 days after the third vaccine dose and 52% against COVID-19–associated hospitalization more than 4 months after the 3rd dose. Among adults aged ≥50 years, COVID-19 vaccine effectiveness against COVID-19–associated hospitalization ≥120 days after receipt of dose 3 was only 32%, increasing to 66% ≥7 days after the fourth dose.[481]

Effect of neutralizing antibodies

One study found that the in vitro concentration (titer) of neutralizing antibodies elicited by a COVID-19 vaccine is a strong correlate of immune protection. The relationship between protection and neutralizing activity is nonlinear. A neutralization as low as 3% (95% CI, 1–13%) of the level of convalescence results in 50% efficacy against severe disease, with 20% (14–28%) resulting in 50% efficacy against detectable infection. Protection against infection quickly decays, leaving individuals susceptible to mild infections, while protection against severe disease is largely retained and much more durable. The observed half-life of neutralizing titers was 65 days for mRNA vaccines (Pfizer–BioNTech, Moderna) during the first 4 months, increasing to 108 days over 8 months. Greater initial efficacy against infection likely results in a higher level of protection against serious disease in the long term (beyond 10 years, as seen in other vaccines such as smallpox, measles, mumps, and rubella), although the authors acknowledge that their simulations consider only protection from neutralizing antibodies and ignore other immune protection mechanisms, such as cell-mediated immunity, which may be more durable. This observation also applies to efficacy against variants and is particularly significant for vaccines with a lower initial efficacy; for example, a 5-fold reduction in neutralization would indicate a reduction in initial efficacy from 95% to 77% against a specific variant, and from a lower efficacy of 70% to 32% against that variant. For the Oxford–AstraZeneca vaccine, the observed efficacy is below the predicted 95% confidence interval. It is higher for Sputnik V and the convalescent response, and is within the predicted interval for the other vaccines evaluated (Pfizer–BioNTech, Moderna, Janssen, CoronaVac, Covaxin, Novavax).[482]

Side effects

All vaccines, including COVID-19 ones, can have minor side effects related to the mild trauma associated with the introduction of a foreign substance into the body.[483][484] These include soreness, redness, rash, and inflammation at the injection site. Other common side effects include fatigue, headache, myalgia (muscle pain), and arthralgia (joint pain) which generally resolve within a few days.[485]

Serious adverse events that follow the administration of vaccines are of high interest to the public.[486] It is important to recognize that the occurrence of an adverse event following vaccination does not necessarily mean that the vaccine caused the adverse event; the health problem may have been unrelated. Reporting of all adverse events, careful followup and statistical analysis of occurrences are required to determine whether or not a specific health problem is more likely to occur after a vaccine is administered.[487][488][489]

More serious side effects are very rare. Before COVID-19 vaccines such as Moderna and Pfizer/BioNTech were authorized for use in the general population, they had to pass phase III studies involving tens of thousands of people. Any serious side effects that did not appear during that testing are likely to occur less often than ~1 in 10,000 cases. It is important that Phase III trials be diverse, to ensure that safety results apply broadly. It is possible that side effects may affect a population that was not adequately represented during the initial testing. Pregnant women, immunocompromised people, and children are usually excluded from initial studies because they may be at higher risk. Further studies may be done to ensure their safety before vaccines are authorized for use in such populations. Subsequent examinations of the use of COVID vaccines in pregnant people and in children have shown similar outcomes to the general population and do not suggest greater risk for these groups.[489]

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