US vaccine monitoring algorithm missed safety alerts despite internal warnings

US health officials continued using a vaccine safety algorithm despite being warned that it could miss potential adverse reactions linked to Covid-19 vaccines, an investigation by The BMJ has found.

The findings are based on government emails released through freedom of information requests and to US Senate investigators, alongside interviews with public health officials and scientists.

The Centers for Disease Control and Prevention and the Food and Drug Administration jointly operate the Vaccine Adverse Event Reporting System, known as VAERS. Before Covid vaccines were introduced in December 2020, officials said the system would help identify possible safety concerns quickly.

However, the statistical method relied upon compared the number of reported reactions following Covid vaccination with the number expected from reports across the wider database. Because more than 90% of early VAERS submissions related to the Pfizer and Moderna vaccines, a reaction occurring at similar rates after both could fail to trigger an automated warning.

FDA medical officer Dr Ana Szarfman and statistician William DuMouchel, who developed the original algorithm, warned senior officials about the problem in early 2021. They proposed a revised method that generated safety signals, but Szarfman was reportedly instructed to “cease and desist”.

The BMJ said the algorithm failed to flag reports involving myocarditis, pericarditis, Bell’s palsy and tinnitus. When the CDC later conducted a different statistical analysis in 2022, hundreds of reported conditions met its alert criteria.

VAERS reports do not prove that a vaccine caused a medical condition. They are intended to identify patterns requiring further investigation, meaning an effective detection system is essential to distinguish genuine risks from coincidental events.

Internal correspondence reviewed by The BMJ reportedly showed that FDA officials understood the limitation before and during the vaccine rollout. DuMouchel said officials were wrong to reject the proposed changes and that the system would have performed better had they acted on Szarfman’s advice.

Stay informed with the stories shaping health and social care.