According to a national survey, more than half of parents with children under age 18 falsely believe that the flu shot can cause the flu. In fact, the inactivated parts of the virus used in the shot help to build up immunity in your system.

Robin S. Jacobson, MD, clinical assistant professor in the Department of Pediatrics and medical director of NYU Langone Pediatric Associates—Irving Place, spoke with Good Housekeeping to dispel this myth. “If the infection comes, your body is already ready to fight it, so you either get over the infection without realizing you had it, or it is not as bad as it would have been without the immunization,” Dr. Jacobson says.

If you sometimes feel sick after getting the flu shot, that’s actually good news because it means your immune system is reacting to the foreign substance that’s been injected, according to Dr. Jacobson. “The reaction is a good sign that the person’s immune system is working the way that it should.”

The immunization takes about two weeks to fully kick in, so doctors recommend you and your family get one as soon as possible.

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