Pfizer COVID-19 Vaccine Shows Continued Efficacy, Safety at 6 Months

Though efficacy waned over months, protection from symptomatic and severe COVID-19 remained significant, with no new adverse event risks observed.

Pfizer-BioNTech COVID-19 vaccine BNT162b2 (Comirnaty) provides high efficacy and a favorable safety profile through 6 months post-administration, according to new data from the Pfizer Vaccine Research and Development team published in The New England Journal of Medicine.

Though investigators observed a gradual decline in efficacy from the 2-dose mRNA vaccine over time, this assessment of data from the collaborating companies’ original pivotal phase 2-3 trial program showed BNT162b2 provides nearly 97% efficacy against severe COVID-19.

Led by Stephen J. Thomas, MD, of the State University of New York, Upstate Medical University, the investigators provided approximate 6-month follow-up trial data on pre-specified outcomes of vaccine efficacy in preventing symptomatic COVID-19 and a defined safety profile. The data was included in Pfizer-BioNTech’s Biologics License Application (BLA) that resulted in US Food and Drug Administration (FDA) approval of the vaccine last month.

In the investigators’ previous assessment of median 2-month post-immunization data from the global trial, the vaccine’s efficacy was approximately 95%, with a generally favorable profile among administered subpopulations.

“These data formed the basis for BNT162b2 emergency or conditional authorizations globally,” they wrote. “Here, we report safety and efficacy findings from a prespecified analysis of the phase 2–3 portion of the trial through approximately 6 months of follow-up. These additional data contributed to the full approval of BNT162b2 in the United States.”

The ongoing, placebo-controlled, observer-blinded, multinational trial randomized 44,165 participants ≥16 years old and 2264 participants 12-15 years old to either a pair of 30 mcg doses of the vaccine administered 21 days apart, or placebo.

Laboratory-confirmed COVID-19 diagnosis after 7 or more days following the second dose was used to define vaccine efficacy versus placebo through a median 6 months of follow-up.

Thomas and colleagues reported that, among the 42,094 participants ≥12 years old eligible for evaluation and without previously evidenced SARS-CoV-2 infection, 77 cases of COVID-19 were observed in vaccine recipients up to the data cutoff date of March 13, versus 850 cases in patients administered placebo—indicating a vaccine efficacy of 91.3% (95% CI, 89,0 – 93.2).

Among the 44,486 eligible participants with or without previous SARS-CoV-2 infection, vaccine efficacy was 91.1% (95% CI, 88.8 – 93.0).

Vaccine efficacy after just 1 dose of BNT162b2 was 58.4% (95% CI, 40.8 – 71.2), based on 46 positive cases in patients between the first and second doses of the vaccine. However, Thomas and colleagues stressed the inability to perceive first-dose protection due to 99% of participants received their second dose as scheduled.

Investigators indeed observed a steady wane in vaccine efficacy over the 6 months: from 7 days to <2 months following the second dose, vaccine efficacy was 96.2%; from 2 months to <4 months, it dipped to 90.1%; from 4 months to the data cutoff date, vaccine efficacy was 83.7%.

Just 1 of the 31 trial participants to report severe COVID-19 symptoms was a vaccine recipient, indicating an efficacy of 96.7% (95% CI, 80.3 – 99.9).

Thomas and colleagues observed benefit derived by the vaccine approximately 11 days following the first dose; vaccine efficacy was 91.7% from that time of immunization onward.

“Early protection against COVID-19 without strong serum neutralization indicates that neutralizing titers alone do not appear to explain early BNT162b2-mediated protection from COVID-19,” they wrote. “Other immune mechanisms (e.g., innate immune responses, CD4+ or CD8+ T-cell responses, B-cell memory responses, and antibody-dependent cytotoxicity) may contribute to protection.”

The safety data, of which more than 12,000 participants have now contributed ≥6 months of follow-up, showed a consistent profile at 6 months as was confirmed in the 2-month assessment. No cases of myocarditis have been observed among vaccinated participants.

“The data in this report show that BNT162b2 prevents COVID-19 effectively for up to 6 months after the second dose across diverse populations, despite the emergence of SARS-CoV-2 variants, including the beta variant, and the vaccine continues to show a favorable safety profile,” investigators concluded.