Study Shows 4.2 Percent of Pfizer COVID Vaccine Batches Made up Most Adverse Events, Raising Serious Concerns

A nurse prepares a COVID-19 vaccine in Sydney, Australia on Oct. 3, 2021. Lisa Maree Williams/Getty Images

In Denmark, 4.2 percent of Pfizer COVID-19 vaccine batches accounted for 71 percent of suspected adverse events (SAEs), according to Danish researchers in a recent study published in the European Journal of Clinical Investigation on March 30.

The study has raised serious concerns about the inconsistencies in the quality of different vaccine batches and the implications for vaccine recipients.

The Study

Danish researchers studied the rates of SAEs between different batches of the Pfizer-BioNTech vaccine, BNT162b2, which was administered in Denmark from December 27, 2020–January 11, 2022.