In-Depth: Why women have more vaccine side effects than men Sex hormones, chromosomes play a role As more Americans get immunized with the COVID-19 vaccines, thereâs a clear trend emerging: women are experiencing more severe side effects. By: Derek Staahl and last updated 2021-04-29 13:04:12-04 SAN DIEGO (KGTV) â As more Americans get immunized with the COVID-19 vaccines, thereâs a clear trend emerging: women are experiencing more severe side effects. Women submitted 78.7 percent of the side effect reports to the Centers for Disease Control and Prevention during the first month of vaccination from Dec. 14 to Jan. 18, the most recent data available. Women got 61.2 percent of the doses in that span.