Toddlers and young children may face a higher risk of seizures shortly after receiving the COVID-19 vaccine, according to a new study conducted by researchers from the U.S. Food and Drug Administration (FDA). The study found that the incidence of febrile seizures was 2.5 times higher among children aged zero to one day after a Moderna shot, compared to the same children eight to 63 days after vaccination. The researchers described this risk as “significantly elevated.” However, the elevated risk for febrile seizures after a Pfizer-BioNTech dose was not statistically significant.
The study, led by Richard Forshee, the deputy director of the FDA's Office of Biostatistics and Pharmacovigilance, analyzed data from commercial databases, including CVS Health, Optum, and Carelon Research. The study focused on children aged 2 to 5 years old.
Fever is a common side effect of COVID-19 vaccines, and the study found that 19 percent of children aged 2 to 3 experienced fever after receiving a second dose of the Pfizer vaccine. Fever can sometimes lead to febrile seizures, which may explain the increased risk observed in the study.
The researchers conducted a self-controlled case series, excluding seizures that occurred two to seven days after vaccination to ensure that the cases were more likely to be associated with vaccination rather than other causes. In the primary analysis, they identified 88 febrile seizures after the Pfizer vaccination and 67 cases after the Moderna vaccination.
In a secondary analysis using a longer risk interval within seven days of vaccination, the researchers identified 103 febrile seizures and 135 seizures/convulsions after Pfizer vaccination and 78 febrile seizures and 106 seizures/convulsions after Moderna vaccination. However, no statistically significant findings were observed in the secondary analysis or any other secondary analyses after adjustments were made to the data.
The study has some limitations, including the small number of cases analyzed. Dr. Harvey Risch, a professor emeritus of epidemiology at the Yale School of Public Health, who was not involved in the research, commented that the small numbers are not large enough for a reliable statistical analysis, making the study scientifically weak.
It is important to note that the study analyzed data from vaccines authorized in 2022 and does not cover the currently available versions of the vaccines from Pfizer, Moderna, and Novavax, which were authorized in late 2023 based on clinical trial data from just 50 humans.
