A vaccine is a medical product. Vaccines, though they are designed to protect from disease, can cause side effects, just as any medication can. When a virus is widely circulating in a population and causing many infections, the likelihood of the virus mutating increases. The more opportunities a virus has to spread, the more it replicates – and the more opportunities it has to undergo changes. Most viral mutations have little to no impact on the virus’s ability to cause infections and disease.
