Pfizer-BioNTech’s KP.2 Covid vaccine shows no new safety signals in 89,000-person study

A real-world analysis found no statistically significant increase in 20 monitored adverse events after the 2024-25 KP.2 mRNA vaccine, including when given alongside seasonal flu vaccination.

A new safety analysis should reassure pharmacists and patients heading into respiratory virus season: the 2024-25 Pfizer-BioNTech KP.2 Covid-19 vaccine was not associated with a higher risk of any of 20 pre-specified adverse events of special interest, according to researchers writing in Vaccine.

The observational study followed 89,485 commercially insured people aged six months and older who received the updated shot between August 2024 and March 2025. Using a self-controlled risk interval design, the researchers compared health events recorded soon after vaccination with later control periods in the same individuals, a method intended to reduce the influence of differences between patients.

The conditions monitored included neurological events, cardiovascular problems, immune-mediated disorders and systemic inflammatory syndromes. Point estimates were slightly higher during the risk window for non-febrile seizures and shingles, but those differences were not statistically significant, and none of the measured outcomes crossed the study’s threshold for a safety signal. More than three-quarters of participants also received a seasonal flu vaccine on the same day, without any change in the overall safety pattern.

The findings add to a broader body of real-world evidence suggesting that updated mRNA Covid-19 vaccines have maintained a safety profile similar to earlier formulations. Other studies have found no meaningful increase in myocarditis or pericarditis signals with variant-adapted shots, while separate effectiveness research has shown that the 2024-25 KP.2 vaccine provided meaningful protection against Covid-19-related death, with the strongest benefit seen in adults aged 75 and older.