Safety of BNT162b2 mRNA COVID-19 Vaccine Batches: A Nationwide Cohort Study.

Objectives: The safety of the BNT162b2 mRNA COVID-19 vaccine has been extensively evaluated since the global rollout began. While serious adverse events are rare, safety issues continue to arise. This study evaluates the claim that earlier small vaccine batches were associated with higher rates of serious adverse events compared to later batches.

Design, participants, setting: A nationwide cohort study was conducted in Denmark, comprising individuals vaccinated with the BNT162b2 vaccine from 52 pre-defined batches classified into three pre-defined groups. Vaccinated individuals were matched 1:1 between batch groups on age, sex, and vaccination priority group. The study outcomes included 27 serious adverse events, two negative control outcomes, and all-cause mortality. Cox regression was used to estimate hazard ratios (HRs) comparing rates between batch groups in the 28 days following vaccination. We conducted two comparisons of the early small batches to two groups of larger batches used later in the pandemic.

Results: In the study period, 9 983 728 vaccinations were administered from batches in the three pre-defined groups. Slightly increased rates of arrhythmia were observed in both study comparisons, HRs 1.25 (95% CI, 1.05-1.50) and 1.15 (1.00-1.31), respectively, but sensitivity analyses did not robustly support these associations. For the remaining outcomes, increased rates in both study comparisons were not observed.

Conclusion: This nationwide cohort study provides reassurance regarding the safety of the BNT162b2 vaccine across different batches used in Denmark. The findings support the overall safety of the vaccine, with no clinically relevant variations in serious adverse event rates between batches.