Vaccines: Why some of us are more likely to experience side effects, and what to do

• Most people who receive a seasonal flu or COVID-19 vaccine experience no or very mild side effects.
• A recent study suggests that individuals who experience more serious side effects from vaccination do so because of subtle differences in their immune systems, which influence the body’s response to vaccines.
• The research took COVID-19 mRNA vaccinations as a case study, and looked at both human participants and mouse models.
• Family physician Clare Thompson, MBBS, further explains what to do if you are concerned about side effects.

A research team from the Center for Vaccinology at the University of Geneva (UNIGE) and Geneva University Hospital (HUG), in Switzerland, recently looked into why some people experience serious side effects post-seasonal vaccination when, in most cases, side effects are mild or even non-existent.

The researchers found that the answer may lie in subtle changes to an individual’s immune system, which influence how their body responds to the vaccine.

The UNIGE and HUG researchers have published their findings in Science Translational Medicine. Some of the funding for the study was granted by the pharmaceutical and biotechnology company Moderna.

Arnaud Didierlaurent, Ing. PhD, associate professor at the Center for Vaccinology at UNIGE and HUG, and in the Department of Pathology and Immunology at the Faculty of Medicine, UNIGE, senior author of the study, explained in a press release:

“Whilst we know that older people tend to experience fewer reactions to vaccination because of age-related declines in immune function, and that the vaccine dose can influence the severity of side effects, the biological mechanisms underlying these individual differences in symptoms have remained poorly understood.”