Question: I read yesterday that the Pfizer vaccination is effective for at least 6 months.  Why only 6 months and what does that mean for booster shots?

Answer: Pfizer released a statement yesterday sharing findings from its updated analysis of its clinical trial, which includes 46,307 trial participants, more than 12,000 of whom have had a follow-up time of at least six months. I’ve bulleted below a few of the key findings (not yet peer reviewed).  We should expect to continue to see analyses like these as the months progress to inform our understanding of the duration of vaccine efficacy.  We can only talk 6 months right now because that’s as long as we’ve been able to have a cohort of folks to follow, *not* because that’s how long we expect vaccines to be effective. When it comes to booster shots, we’ll need them if: a) efficacy/effectiveness substantially wanes over time; and/or b) a new variant arises that evades vaccinated individuals’ immune response.            

• The vaccine remains highly efficacious over time.  “From the 927 confirmed symptomatic cases of COVID-19 in the trial, 850 cases of COVID-19 were in the placebo group and 77 cases were in the BNT162b2 [vaccination] group, corresponding to vaccine efficacy of 91.3% (95% confidence interval [CI, 89.0, 93.2]).”
• It protects against severe disease for at least six months.  “Thirty-two cases of severe disease, as defined by the CDC, were observed in the placebo group versus none in the BNT162b2 vaccinated group, indicating that the vaccine was 100% efficacious in this analysis against severe disease by the CDC definition (95% CI, [88.0,100.0]).”
• It protects against the B.1.351 variant (South Africa).  “In South Africa, where the B.1.351 lineage is prevalent and 800 participants were enrolled, nine cases of COVID-19 were observed, all in the placebo group, indicating vaccine efficacy of 100% (95% CI, [53.5, 100.0]). In an exploratory analysis, the nine strains were sequenced and six of the nine were confirmed to be of the B.1.351 lineage. These data support previous results from immunogenicity studies demonstrating that BNT162b2 induced a robust neutralizing antibody response to the B1.351 variant…”
• It is safe. “No serious safety concerns were observed in trial participants up to six months after the second dose.”