Viral Claims About Vaccine Side Effects Are Misleading

A viral Facebook post claims that Pfizer has recently released a long list of side effects to its COVID-19 vaccine. “PFIZER JUST RELEASED ITS LIST OF SIDE EFFECTS OF ITS ‘COVID VACCINE,’” the post says. It goes on to list more than 40 supposed side effects of the vaccine including conditions like heart failure, liver damage, stillbirth, and sudden death. Some of the posts have been shared thousands of times across Facebook over the last week.

The post is misleading. The conditions listed were included in a 2021 adverse event analysis sent by Pfizer to the Food and Drug Administration (FDA), but that does not indicate that they are “side effects” of the COVID-19 vaccine.

Following the emergency-use authorization of Pfizer’s COVID-19 mRNA vaccine in the United States, Pfizer submitted an analysis of adverse event reports (AERs) made worldwide by recipients of the vaccine as part of the vaccine’s full approval process. The analysis, which was sent to the FDA in February 2021, examined 158,893 adverse events reported in 63 countries and included any negative medical events or conditions reported by vaccine recipients in the months following their vaccination.

While AERs are used to monitor whether drugs are safe in the general population, their uses are limited and do not necessarily indicate that the adverse events reported are caused by the drug in question. According to the FDA, the agency “does not require that a causal relationship between a product and event be proven,” and “​​there is no certainty that [a] reported event (adverse event or medication error) [is] due to the product.” Pfizer reiterates this point in its own report, saying that “An accumulation of [AERs] does not necessarily indicate that a particular [adverse event] was caused by the drug; rather, the event may be due to an underlying disease or some other factor(s) such as past medical history or concomitant medication.”

This differentiation is not unique to the COVID-19 vaccine—uncorrelated adverse events are recorded for all vaccines evaluated by health authorities. “Anytime a large vaccine trial is done, any adverse event that is reported in the vaccine group, independent of whether it’s reported at the same level in the placebo group, will end up being recorded as a vaccine adverse event, even though it’s not causally associated, it’s just coincidence,” Dr. Paul Offit, director of the Children’s Hospital of Philadelphia’s Vaccine Education Center, told The Dispatch Fact Check. 

For example, if a person receives their first dose of the COVID-19 vaccine on Monday, then breaks their leg on Tuesday, that bone fracture may be reported as an adverse event related to the COVID-19 vaccine even if the fracture wasn’t related to the vaccine itself. Similarly, if a person begins taking a new medication the same week as receiving the COVID-19 vaccine, an adverse event caused by the medication might also be recorded as an adverse event related to the vaccine.

According to Offit, this uncertainty is why adverse event reporting is not useful for determining the actual side effects of a drug. “The vaccine adverse events report system doesn’t allow you to do that … It in no way enables you to determine whether that problem was caused or associated with a vaccine,” Offit explained. “Nonetheless, people often jump on this as evidence that a vaccine was harmful, but it wasn’t.”

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