Health experts explained why women report more side effects after receiving the COVID-19 vaccine than men. (Photo : Milos Bicanski/Getty Images) A woman receives a dose of the Moderna vaccine against the coronavirus disease. Women Reports More Side Effects From December 14 to January 13, almost 7,000 cases were processed through the Centers for Disease Control and Prevention's Vaccine Adverse Effect Reporting System, with more than 79 percent of them coming from women. Headache, nausea, and dizziness were the most often recorded side effects. Women are much more likely than men to suffer some of the vaccine's more unusual side effects, such as an itchy red rash at the injection site known as the COVID arm or Moderna arm, since the Moderna vaccine accounts for about 95 percent of the reactions. Women account for 77 percent of the confirmed side effects of the Moderna vaccine, according to a published article in The USA Today.