The Pfizer-BioNTech COVID-19 vaccine: remarkably effective

The rapid development of SARS-CoV-2 vaccines is one of the few bright spots of 2020. The lipid nanoparticle-formulated, nucleoside-modified mRNA vaccine developed by BioNTech and Pfizer, BNT162b2, is among the most anticipated vaccines. Researchers have examined the safety and efficacy of a regimen of two 30-µg doses in a multinational placebo-controlled, industry-sponsored trial.

The trial enrolled 43,548 participants who were 16 or older. The vaccine's efficacy against confirmed COVID-19 at least 7 days after the second dose was 95%, and appeared to be consistent by age, sex, ethnicity, body-mass index, and presence of preexisting conditions. The study was not designed to assess single-dose efficacy, but COVID-19 incidence in vaccine versus placebo recipients began to diverge 12 days after the first dose. Side effects included mild-to-moderate fever, fatigue, headache, chills, muscle or joint pain, and diarrhoea. All were more frequent after the second dose and generally resolved 1 to 2 days after immunisation.

These findings demonstrate the startlingly high efficacy of the Pfizer-BioNTech vaccine that may arise from induction of both humoral and cellular responses through the mRNA platform. That nine of the ten severe COVID-19 cases were in the placebo group diminishes concern about potential vaccine-induced disease enhancement.

The authors note that the study was not powered to detect adverse effects with incidence (0.01%, but the safety profile appears similar to that of other licensed vaccines. We still need information about the vaccine's safety; its efficacy in children, pregnant women, and immunocompromised individuals; whether it protects against asymptomatic infection and limits contagiousness; and its durability. Still, the introduction of this and other COVID-19 vaccines provides hope that the pandemic's end is on the horizon.