Vaccine Side Effects: Why Reactions Vary Among Us

A team from UNIGE and HUG reveals why some people develop more pronounced transient symptoms following mRNA vaccination against COVID-19.

Redness and pain at the injection site, fever, fatigue or headaches: vaccines can cause side effects, but their frequency and severity vary considerably from person to person. Why? A team from the Center for Vaccinology at the University of Geneva (UNIGE) and Geneva University Hospital (HUG) has found that, even before vaccination, some people's innate immune systems are more reactive than others, showing a heightened response to interferons, key molecules involved in antiviral defence naturally produced by the body. The stronger this response, the more likely individuals are to experience these transient symptoms. These findings have been published in Science Translational Medicine.