In a Letter to the Editor published in the New England Journal of Medicine (NEJM) on July 20, epidemiologist Dr. Tracy Høeg, physician-scientist Dr. Vinay Prasad, and Dr. Ram Duriseti from Stanford School of Medicine stated that a 2021 Israeli study on Pfizer’s COVID-19 booster may have overestimated the vaccine’s effectiveness by concluding those who received a booster had 90 percent lower mortality due to COVID-19 than non-boosted participants.
The group analyzed deaths attributed to COVID-19 in both the 2021 study and in a later statement by the same study authors to estimate mortality not associated with the virus based on a person’s vaccination status. The mortality unrelated to COVID-19 in the boosted group was compared to mortality unrelated to COVID-19 in the non-boosted group.
The authors found a 94.8 percent lower mortality unrelated to COVID-19 among participants in the boosted group and a “markedly lower incidence of adverse health outcomes” in the same group. Additionally, COVID-19 mortality, whether boosted or not, was essentially the same in the 2021 study, generating a “strong concern” vaccine efficacy was overestimated.
In other words, an individual’s underlying health plays a significant role in COVID-19-related mortality. If the boosted group had fewer health conditions that weren’t accounted for in the data, it wouldn’t be accurate to attribute lower mortality to a third dose of Pfizer’s vaccine.
In a July 20 statement on Twitter, Dr. Høeg said she and her co-authors showed strong evidence of “healthy vaccinee bias” in the Israeli study on boosters that wasn’t disclosed, which could explain “all reported benefits of the booster.”
“No study is perfect, but this one should be retracted,” Florida Surgeon General Dr. Joseph A. Ladapo said in a statement on Twitter. Dr. Ladapo congratulated the letter’s authors for showing that the 90 percent benefit attributed to boosters in the NEJM’s study was “entirely due to selection bias” and demanded randomized controlled trials.
Although the authors said Israel has not been transparent with the data used in their studies, they believe “healthy vaccinee bias” may also have led to overestimates of vaccine effectiveness in other studies.
