Which Covid vaccines completed phase 3 trials in 2020 and what were their efficacy rates?
Executive summary
In 2020 several COVID‑19 vaccine candidates completed large phase‑3 (or phase‑2/3 seamless) trials and reported high efficacy against symptomatic disease: Pfizer–BioNTech’s BNT162b2 reported about 95% efficacy after two doses (phase 2/3 data published in NEJM) [1] [2], and Moderna’s mRNA‑1273 and Oxford–AstraZeneca’s ChAdOx1 had their phase‑3 programs reported in 2020/early 2021 and are discussed across reviews of phase‑3 results (overview of mRNA, viral‑vectored and inactivated vaccine phase‑3 data is summarized in systematic reviews) [3] [4]. Multiple systematic reviews and clinical summaries note that by late 2020 at least six vaccine candidates reached phase‑3 evaluation and several produced efficacy results that led to emergency authorizations [5] [6].
1. Which vaccines reached phase‑3 in 2020 — the quick accounting
The literature and reviews show dozens of candidates entered clinical testing in 2020 and a meaningful subset reached phase‑3 that year. Reviews cite that 27 candidates were in phase‑3 by mid‑pandemic and that six vaccines (including two mRNA, two inactivated and two viral‑vectored platforms) had efficacy data from phase‑3 leading to emergency use or conditional approvals by the end of 2020/early 2021 [5] [6]. Systematic reviews compiling phase‑3 publications through mid‑2021 list trials for mRNA vaccines (BNT162b2, mRNA‑1273), adenoviral vectored vaccines (ChAdOx1 nCoV‑19/AZD1222, Ad26), and multiple inactivated vaccines (CoronaVac, BBIBP‑CorV) as among those with phase‑3 results or interim reports [3] [4].
2. Pfizer–BioNTech (BNT162b2): the headline 95% result and what it covered
Pfizer’s global phase‑2/3 trial enrolled tens of thousands and the peer‑reviewed NEJM report and regulatory summaries documented ~95% efficacy in preventing symptomatic COVID‑19 seven days after the second dose in the originally reported analysis; that finding underpinned emergency authorizations in December 2020 [1] [2]. The trial was designed with sequential analyses and a high success boundary to control type‑I error; it focused on virologically confirmed, symptomatic disease as the primary endpoint [1] [7].
3. Moderna (mRNA‑1273) and others: similar platform, similar timing
Systematic reviews and phase‑3 syntheses list Moderna’s mRNA‑1273 among the mRNA candidates that completed pivotal testing with high efficacy estimates reported around the same period; mRNA vaccines as a class were prominent among the early successful programs [3] [4]. Specific efficacy figures for Moderna are described across reviews of phase‑3 trials rather than in the single NEJM Pfizer paper cited here [3] [4]. Available sources do not mention a single, exact Moderna phase‑3 efficacy number in these snippets; they document that mRNA‑1273 had positive phase‑3 results summarized in later comprehensive analyses [3].
4. Adenoviral vector and inactivated vaccines: heterogeneity in results and reporting
Adenovirus‑vectored vaccines (Oxford–AstraZeneca ChAdOx1 and others) and inactivated vaccines (CoronaVac, BBIBP‑CorV) completed large trials with efficacy estimates that varied by study site, dosing regimen and endpoint definitions; systematic reviews and meta‑analyses collected those disparate results [3] [4] [8]. Reviews note it is difficult to directly compare point estimates across trials because of differing case definitions, populations and timing [9] [8].
5. How to read the headline efficacy numbers: endpoints, timing and real‑world gaps
Phase‑3 trials were primarily designed to measure individual‑level efficacy against symptomatic, PCR‑confirmed COVID‑19 over the blinded follow‑up period; they were not principally powered to measure transmission or the long‑term durability of protection, which regulatory documents and fact‑checks emphasize [7] [2]. Trial designs used seamless/combined phase approaches and sequential interim analyses that allowed early stopping once efficacy was demonstrated [6] [10].
6. Limitations, disagreements and what the reviews say
Systematic reviews warned of heterogeneity across trials (different designs, sample sizes, case definitions and sites), which complicates direct efficacy comparisons [3] [8]. Regulatory and fact‑checking sources stress that initial trials focused on symptomatic disease and short‑term protection; questions about protection against asymptomatic infection, transmission, variant strains and durability were left to later study [2] [7].
7. Bottom line for the reader
Peer‑reviewed phase‑3 data from 2020 firmly established high efficacy for Pfizer–BioNTech’s BNT162b2 (~95% vs symptomatic COVID‑19 in the originally reported analysis) and placed other platforms (Moderna mRNA, adenoviral vectored and inactivated vaccines) in the same rapid‑success cohort; systematic reviews catalog the set of phase‑3 trials and underscore important differences in methods and endpoints that limit head‑to‑head comparisons [1] [3] [5] [6]. Available sources do not provide a single table of every vaccine and every 2020 phase‑3 efficacy number in these snippets; for exact point estimates for each candidate you should consult the individual phase‑3 publications and the systematic reviews cited above [3] [4].