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Safety and Efficacy of BNT162b2 mRNA COVID-19 Vaccine
Quick Takes
- The Pfizer/BioNTech mRNA vaccine (BNT162b2) was 95% efficacious at preventing COVID-19 at 2 months in a clinical trial of >40,000 participants.
- Efficacy was 52% after the first dose, and reached >90% 7 days after the second dose.
- There were no increases in serious adverse events with the vaccine compared to placebo.
Study Questions:
How safe and effective is the BNT162b2 mRNA vaccine for preventing coronavirus disease 2019 (COVID-19)?
Methods:
BNT162b2 is a vaccine produced by Pfizer and BioNTech based on lipid nanoparticle–formulated nucleoside-modified RNA encoding the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) full-length spike protein. The safety and efficacy of the vaccine was studied in a phase 2/3 clinical trial in which 43,448 participants ages ≥16 years were randomized to either a two-dose regimen of BNT162b2 or placebo. The doses of vaccine were administered 21 days apart. The primary endpoint was efficacy against confirmed COVID-19 defined as the presence of symptoms and positive test for SARS-CoV-2 within 4 days of the symptomatic period. The major secondary endpoint was severe COVID-19, defined as severe systemic illness, organ failure, admission to the intensive care unit, or death. Median follow-up time was 2 months. The analysis included all participants who received at least one dose of BNT162b2 or placebo.
Results:
Of the 43,448 participants who received injections, 37,706 had ≥2 months of safety data available. Among these 37,706 participants, 49% were female, 83% were White, 9% were Black or African American, 28% were Hispanic or Latin, and 35% were obese. The median age was 52 years, and 42.3% were aged ≥55 years. Regarding efficacy, eight cases of COVID-19 with onset ≥7 days after the second dose were observed among vaccine recipients and 162 among placebo recipients, which translates to a 95.0% vaccine efficacy (95% confidence interval [CI], 90.3-97.6). There were no significant differences in efficacy across age, sex, race, ethnicity, obesity, and the presence of hypertension. Between the first dose and the second dose, 39 cases in the BNT162b2 group and 82 cases in the placebo group were observed, resulting in a vaccine efficacy of 52% (95% CI, 29.5-68.4) during this interval and indicating early protection by the vaccine, starting as soon as 12 days after the first dose. Common reactions were pain at the injection site (>80%), fatigue, and headache (~55%). Overall, more BNT162b2 recipients than placebo recipients reported any adverse event (27% and 12%, respectively) or a related adverse event (21% and 5%). No deaths were considered by the investigators to be related to the vaccine or placebo and no COVID-19–associated deaths occurred.
Conclusions:
The two-dose regimen of the BNT162b2 mRNA vaccine (Pfizer/BioNTech) was 95% efficacious at preventing COVID-19 at 2 months with no increased risk of serious adverse events compared to placebo.
Perspective:
Currently, 48 vaccines are under clinical study, of which 11 are under evaluation in phase 3 clinical efficacy studies. This report follows closely the one from Oxford/AstraZeneca showing an efficacy of 70% for the viral vectored ChAdOx1 nCoV-19 vaccine. The Pfizer/BioNTech trial, however, had enrolled 3 times more participants compared to the Oxford/AstraZeneca studies combined. Follow-up time was similar between both reports (2 months for BNT162b2 and 3.4 months for ChAdOx1). Participants who received the BNT162b2 vaccine were older, with >40% of participants >55 years old, while only 12% of those who received the ChAdOx1 were >55 years old. The participant population of the Pfizer/BioNTech vaccine is more representative of the population at higher risk of COVID-19 due to their relatively older age. An efficacy of 95% for the BNT162b2 mRNA vaccine for safely preventing COVID-19 in this population is highly reassuring. The short follow-up time and the lack of systematic testing for SARS-CoV-2 as part of the protocol leaves important questions unanswered with regard to the intermediate long-term effectiveness of the vaccine, the potential occurrence of rare but more serious side effects, and whether the vaccine can prevent asymptomatic transmission.
Clinical Topics: COVID-19 Hub, Prevention, Hypertension
Keywords: Coronavirus Infections, COVID-19, Ethnic Groups, Fatigue, Headache, Hypertension, Obesity, Primary Prevention, RNA, Messenger, severe acute respiratory syndrome coronavirus 2, Spike Glycoprotein, Coronavirus, Vaccination, Viral Vaccines
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