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Experts say the estrogen in women’s bodies produces a stronger immune system reaction to vaccinations. MCKINSEY JORDAN/Stocksy
  • Researchers at the CDC say women tend to have stronger side effects to COVID-19 vaccines than men.
  • Experts say this isn’t unusual with vaccinations because the estrogen in women’s bodies is designed to elicit a stronger immune response.
  • They add that women still shouldn’t hesitate to get the COVID-19 vaccine because the potential consequences of the disease are far worse than the vaccination side effects.

Frontline workers Shelly and Scott Blomgren were among the first people in the United States to get the COVID-19 vaccine in January.

The afternoon after their second shot of the Moderna vaccine, it was clear to Shelly that their reactions to the vaccine were remarkably different.

“He was fine,” she told Healthline. “Me? I was dying. I’m a tough cookie. I can take pain. But this was awful.”

Blomgren said she struggled for almost 2 days with “the worst body aches I’ve had in my life,” along with chills, fever, and exhaustion, while her husband went on with his work and life with just a few chills.

Two days later, they were both fine and fully vaccinated.

What the Blomgren’s experienced is apparently repeating itself in many homes across the nation.

A report released by the Centers for Disease Control and Prevention (CDC) found that of the first 13.8 million COVID-19 vaccine doses given to Americans, reports of side effects were coming at a higher rate from females.

In fact, 79 percent of side effects reported came from women, although only 61 percent of the vaccines were given to women.

The study results aren’t concerning to infectious disease experts.

They point out that a stronger response from women to other vaccinations has been seen for years.

The reason?

Experts suspect that in women, particularly premenopausal women, the levels of estrogen help activate the immune response to illness and, therefore, to vaccines.

Men, on the other hand, have more testosterone, a hormone that can somewhat dampen or slow down the same response.

Simply put, women in general have a stronger response to vaccines because their bodies are quicker and stronger when it comes to activating what the vaccine introduces in the body.

“Infectious diseases in general are always about the immune response and not the bug,” said Dr. Larry Schlesinger, president and chief executive officer of the Texas Biomedical Research Institute in San Antonio.

“In women, there is an exuberant and stronger response [to many vaccines],” he told Healthline. “There’s actually a lot of science behind this.”

In the past, Schlesinger said, a stronger response in females has been seen and studied in vaccines for yellow fever, DPT, influenza, and other illnesses.

Schlesinger said estrogen encourages the body to produce more T-cells, the reactor cells that protect us, when a vaccine is introduced.

Thus, he said, we see the quicker and stronger response many women experience.

The challenge now is to share this information while not raising concerns or reasons to avoid the COVID-19 vaccine, experts say.

Dr. William Schaffner, infectious disease expert and professor in the division of infectious diseases at Vanderbilt University School of Medicine in Tennessee, told Healthline that this is “an understudied phenomenon” that’s been noticed for years.

He urges women to understand that a stronger response and temporary symptoms are not a reason to turn the vaccine away.

“COVID-19 is bad and it will put women into the ICU just as it does men,” Schaffner said.

Side effects to the vaccine, he added, “are transient and mostly gone in 24 hours.”

Schlesinger said that for many women, the vaccine is a “two-edged sword.”

On one side you have evidence that women get a robust antibody response to it, which, he said, “with COVID is exactly what we want.”

On the other side, he said, is the potential for a day or so of suffering.

Julianne Gee, MPH, a lead author of the study and a medical officer in the CDC’s Immunization Safety Office, told Healthline that the study, which is part of the CDC’s ongoing tracking of the vaccines and their impact, should not sway anyone from taking a shot.

“COVID-19 disease can cause serious complications and even death, and vaccination is an important prevention tool to prevent disease and complications,” she said. “COVID-19 vaccines will help society return to normal.”

Schaffner agreed.

“Roll up those sleeves,” he said. “[These vaccines] are effective and we need them for our short-term goals (of getting somewhat back to normal) as well as for our long-time protection.”

Blomgren said even with the difference in her reaction compared to her husband, she’d not hesitate to be vaccinated.

“I was never concerned,” she said. “It’s just what I had to go through to get to where I am now, and to help get us to where we all need to be.”