SARS-CoV-2 Vaccination — An Ounce (Actually, Much Less) of Prevention -NEJM editorial

From the Editorial

‘We are publishing today in the Journal the results of a phase 3, double-blind, randomized, controlled trial of a new RNA vaccine.1 In this trial, 21,720 participants received BNT162b2 and 21,728 received placebo. Both groups received two injections spaced 21 days apart. Persons with obesity or other coexisting conditions were well represented, and more than 40% of participants were older than 55 years of age. Participants notified trial sites if they had symptoms that were consistent with Covid-19, and they were tested to diagnose infection.

The primary outcomes were safety and the incidence of symptomatic Covid-19 with onset occurring at least a week after the second dose of vaccine or placebo, although all symptomatic infections are reported.

The findings in this report include the first 170 cases of Covid-19 detected in the primary population and cover a median of 2 months of safety data. The investigators plan to continue to follow the participants, although once the vaccine becomes freely available, maintaining randomization may be a challenge.

The results were impressive. In the primary analysis, only 8 cases of Covid-19 were seen in the vaccine group, as compared with 162 in the placebo group, for an overall efficacy of 95% (with a 95% credible interval of 90.3 to 97.6%).

Although the trial does not have the statistical power to assess subgroups, efficacy appeared to be similar in low-risk and high-risk persons, including some from communities that have been disproportionately affected by disease, and in participants older than 55 years of age and those younger than 55.

Adverse events were largely consistent with vaccine reactogenicity, with mostly transient and mild local reactions such as injection-site pain and erythema; systemic reactions such as fever, fatigue, and adenopathy were uncommon. This pattern appears to be similar to that of other viral vaccines and, at least with this number of participants and this follow-up period, does not arouse specific concern.

Important questions of course remain. Only about 20,000 people have received this vaccine. Will unexpected safety issues arise when the number grows to millions and possibly billions of people? Will side effects emerge with longer follow-up? Implementing a vaccine that requires two doses is challenging. What happens to the inevitable large number of recipients who miss their second dose? How long will the vaccine remain effective? Does the vaccine prevent asymptomatic disease and limit transmission? And what about the groups of people who were not represented in this trial, such as children, pregnant women, and immunocompromised patients of various sorts?

Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine


Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and the resulting coronavirus disease 2019 (Covid-19) have afflicted tens of millions of people in a worldwide pandemic. Safe and effective vaccines are needed urgently.


In an ongoing multinational, placebo-controlled, observer-blinded, pivotal efficacy trial, we randomly assigned persons 16 years of age or older in a 1:1 ratio to receive two doses, 21 days apart, of either placebo or the BNT162b2 vaccine candidate (30 μg per dose). BNT162b2 is a lipid nanoparticle–formulated, nucleoside-modified RNA vaccine that encodes a prefusion stabilized, membrane-anchored SARS-CoV-2 fulllength spike protein. The primary end points were efficacy of the vaccine against laboratory-confirmed Covid-19 and safety.


A total of 43,548 participants underwent randomization, of whom 43,448 received injections: 21,720 with BNT162b2 and 21,728 with placebo. There were 8 cases of Covid-19 with onset at least 7 days after the second dose among participants assigned to receive BNT162b2 and 162 cases among those assigned to placebo; BNT162b2 was 95% effective in preventing Covid-19 (95% credible interval, 90.3 to 97.6). Similar vaccine efficacy (generally 90 to 100%) was observed across subgroups defined by age, sex, race, ethnicity, baseline body-mass index, and the presence of coexisting conditions. Among 10 cases of severe Covid-19 with onset after the first dose, 9 occurred in placebo recipients and 1 in a BNT162b2 recipient. The safety profile of BNT162b2 was characterized by short-term, mild-to-moderate pain at the injection site, fatigue, and headache. The incidence of serious adverse events was low and was similar in the vaccine and placebo groups.

CONCLUSIONS A two-dose regimen of BNT162b2 conferred 95% protection against Covid-19 in persons 16 years of age or older. Safety over a median of 2 months was similar to that of other viral vaccines. (Funded by BioNTech and Pfizer; number, NCT04368728.)


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