The best way to answer this question, we must define what is “safe”. Like all medicines, vaccines have side effects, such as pain, tenderness or redness at the site of injection. Nothing is harmless. Anything we put into our bodies (like vitamins or antibiotics) can have side effects. So, a more reasonable definition of “safe” would be that the benefits of the vaccine must clearly outweigh the risks. For each vaccine recommended for children, the benefits far outweigh the risks.