Adverse reactions following live attenuated vaccines are similar to a mild form of the natural disease. Adverse reactions following inactivated vaccines are mostly local and may occur with or without fever.

An adverse reaction is any unwanted effect caused by the vaccine. You also may hear adverse reactions called “side effects.” The type of adverse reaction depends on the type of vaccine given. Let’s consider a couple of examples.

MMR: A Live Attenuated Vaccine
MMR is a live attenuated vaccine, which can cause systemic adverse reactions. Because measles causes a rash and fever, the most common adverse reactions after MMR vaccination are a mild rash and fever.

DTaP: An Inactivated Vaccine
DTaP is an inactivated vaccine, which does not replicate in the body. Reactions usually are local at the injection site, e.g., pain, swelling, and redness. Any fever usually occurs because of inflammation at the injection site.

Click here to learn more about adverse reactions to vaccines.