A vaccine is a medical product. Vaccines, though they are designed to protect from disease, can cause side effects, just as any medication can. Most side effects from vaccination are mild, such as soreness, swelling, or redness at the injection site. Some vaccines are associated with fever, rash, and achiness. Serious side effects are rare but may include seizures or life-threatening allergic reaction. All vaccines have the potential to cause side effects in some people, the reality is that most tend to be mild and don't last longer than a few days. The side effects of vaccination definitely weigh on parents' minds. It may be reassuring to know that vaccines are constantly studied and monitored to make sure they are safe. Safety monitoring and testing continue long after vaccines are licensed. The risks of vaccines are much lower than the risks of the diseases that they prevent. The most common vaccine side effects are mild and may include temporary pain, redness or swelling in the area where the shot was given, and flu-like symptoms. Serious side effects from immunization are very rare.