Vaccines do not make a mild illness worse
A child’s immune system is able to respond to millions of antigens every day. Antigens are things like bacteria and viruses that cause your child’s body to produce antibodies against them. Vaccines have only a tiny fraction of the antigens that children encounter naturally. So, the immune system can handle getting vaccines to build immunity to diseases and fight minor illnesses at the same time.
Vaccines do not make symptoms of illness worse—though they may cause mild side effects, like a mild fever or soreness or swelling where the shot was given. To help with discomfort from these side effects, put a cool, wet washcloth on the sore area or ask your child’s doctor about using pain- or fever-reducing medicine.