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KANSAS CITY, Mo. (WDAF) — More women are reporting side effects from COVID-19 vaccines than men, according to the U.S. Centers for Disease Control and Prevention.

The CDC report said women made up 79.1% of the 6,994 people who reported side effects. The analysis is based on the first 13.7 million shots given in the U.S.

Dr. Darrin D’Agostino, executive dean of Kansas City University, said the findings are not surprising.

“We’ve known for years that women tend to react stronger to vaccines. We see that in just about all of the vaccines that we give,” D’Agostino said. “So this is not so much a surprise.”

D’Agostino said there are several reasons why women have stronger side effects:

  • Behavior: Women tend to be more likely to report side effects.
  • Health-conscious: They see doctors more often, and they pay attention to their health a little bit more than men do.
  • Biology: Estrogen drives the immune system in women twice as much as in men.
  • Genetics: The immune system resides on the X chromosome, and women have two, compared with men, who have one.
  • Dosage could be high: Women tend to absorb medications better than men do.

If you have a severe reaction of any kind to the COVID-19 vaccine, or if you experience a minor reaction for more than a couple of days, contact your doctor. If the reaction is potentially life-threatening, go to a hospital.