Q&A on the 2024-2025 COVID-19 Vaccines - FactCheck.org

The updated vaccines have not been specifically tested for safety in people, just as flu vaccines are not tested in people every year with a strain change. The safety of the shots, however, has been well established in the original trials and through surveillance of billions of highly similar doses.

The main serious safety risk of each of the vaccines is inflammation of the heart muscle or its surrounding tissue, known as myocarditis and pericarditis, respectively. The conditions are rare, most commonly affecting young men after a second dose.

Studies have shown that for most people, myocarditis is much more likely following a COVID-19 infection than a COVID-19 vaccine. Infection-related myocarditis is also more severe and linked to worse outcomes.