PITTSBURGH (KDKA) - With the COVID-19 vaccine, Kerri Richardson had delayed side effects.

"I had side effects on both vaccine one and two. My arm was sore. No other side effects until day ten. I then woke up with a rash underneath the injection site," she says.

She wasn't surprised, though.

"I know a few other ladies that have had it, so I was a little warned before," she says.

Turns out, women are more likely to report side effects.

"Patients having the sore arm and the rash, it has been definitely predominantly women that have complained of those side effects," says Samantha Spitzarella, a pharmacist at Asti Drug. "I don't -- can't think of a man that's shared with me that he got the rash, the COVID rash."

The CDC analyzed the safety data from the first 14 million COVID-19 vaccine doses. Women got 61 percent of the vaccines, but reported nearly 80 percent of the side effects. And nearly all of the severe allergic reactions have been in women.

"Women tend to be more sensitive to things like this, so it seems, yeah, probably hormone related," Spitzarella adds.

"It appears, at least in some lab data, that the higher level of estrogen hormone, which of course is the case in women, contribute to more aggressive antibody responses," says Dr. Paul Weinbaum, an OBGYN at the Allegheny Health Network.

Also, the male hormone testosterone can suppress antibody response. Because women have less testosterone, their bodies can generate more of these protective immune system proteins.

"And presumably there's a correlation between the antibody response perhaps and the degree of side effects," Dr. Weinbaum explains.

In studies with flu vaccines, allergic reactions are four times more common in women. Other studies show women account for 80% of all vaccine-related anaphylactic episodes in adults.

Kerri isn't bothered she got a rash. She figures it was just lady's luck.
"Our bodies work differently, so we're going to react differently. By the next day it was completely gone," she said.

It was a slight nuisance for full protection.