A document on the FDA website shows that two participants died as a result of “serious adverse events” from an experimental COVID-19 vaccine.

There were two deaths among the 21,000 participants in the study who got Pfizer and BioNtech's COVID-19 vaccine, however those deaths were not attributed to the vaccination by the US Food and Drug Administration. According to a December 2020 FDA document reporting the fatalities, "one suffered a cardiac collapse 62 days after immunization #2 and died three days later, while the other died from arteriosclerosis three days later." In the instance of the second fatality, the individual had "baseline obesity and pre-existing atherosclerosis", or a narrowing of the arteries, according to the paper.

Four fatalities were also recorded among the 21,000 study participants who got a placebo. The fatalities "reflect occurrences that occur at a similar rate in the general population of the age categories where they occurred", according to the FDA paper. To assess the vaccine's safety, the study documented "severe adverse events", which are defined by the US National Library of Medicine as any medical occurrence that results in death, hospitalization, or significantly interferes with daily living functions. According to the FDA filing, only two adverse events identified in the Pfizer/BioNTech study were thought to be attributable to the vaccine: a shoulder injury and enlarged lymph nodes, a common and normally benign illness.