More women reported side effects, even serious reactions, after getting their COVID-19 vaccines. A recent study by the Centers for Disease Control and Prevention found that 80% of the 7,000 people who reported side effects from the drugs were women.

According to The New York Times, the study published last month analyzed data from the first 13.7 million COVID-19 vaccine doses given in the U.S. The research showed that 79.1% of the reported side effects came from women even though only 61.2% of them received the shot.

Severe adverse reactions such as potentially deadly anaphylaxis were almost always reported by women, said the researchers, adding that the 19 individuals who suffered anaphylaxis after the Moderna shot were female, as were 44 of the 47 who had the reaction after Pfizer’s drug.

Experts say that this new information is consistent with previous studies, according to the Times.

“I am not at all surprised,” said Sabra Klein, a microbiologist and professor at the Johns Hopkins Bloomberg School of Public Health. She has extensively researched how sex and gender impact the human immune system. “This sex difference is completely consistent with past reports of other vaccines.”

A 2013 study by the CDC and other scientists found that women were four times more likely to report allergic reactions than men after receiving the 2009 pandemic flu vaccine. Other studies have also demonstrated that women are 80% more apt to suffer anaphylactic reactions to vaccines, according to the Times.

According to Business Insider, the CDC stated that nearly 7,000 Americans reported vaccine side effects that included headaches, fatigue, and dizziness.

Klein said women should not worry about the likelihood of side effects as this means “you are mounting a very robust immune response, and you will likely be protected as a result,” she told the Times.