This Is Why Half of People Have Stronger Vaccine Side Effects, CDC Says

Allie Hogan
·3 min read

With millions of people getting the COVID vaccine daily, we continue to learn more about potential side effects of the shot. As it turns out, the experience is vastly different between different people, and health experts are trying to learn why. One recent study from the Centers for Disease Control and Prevention (CDC) has found that a certain group of people are having stronger reactions to the vaccine than others. Read on to see if you fall into the half of people having a more noticeable reaction to the coronavirus vaccine, and for more vaccine guidance from the CDC, The CDC Just Gave This New Warning About Your Second COVID Shot.

Women are experiencing stronger vaccine side effects than men.

A Feb. 19 study from the CDC found that women tend to have stronger side effects from the COVID vaccine than men. According to the study, 79 percent of reported side effects came from women. Only 61 percent of the vaccines were given to women, which means women are disproportionately experiencing side effects from the shot.

The most common side effects reported by women were headache (22 percent), fatigue (17 percent), and dizziness (17 percent). The median age of women reporting adverse effects following their shot was 42 years old. And for more on vaccine safety, Don’t Do This Two Hours Before or After Your Vaccine, Doctors Warn.

Experts think women are having stronger side effects due to estrogen.

According to Healthline, experts suspect that women's estrogen levels are the reason they're experiencing stronger vaccine side effects. Estrogen helps activate the immune response to illnesses, and therefore to vaccines as well. On the other hand, men tend to have higher levels of testosterone, which could have the opposite effect, actually dampening or slowing immune response. "In women, there is an exuberant and stronger response [to many vaccines]," Larry Schlesinger, MD president and chief executive officer of the Texas Biomedical Research Institute in San Antonio, told Healthline. "There’s actually a lot of science behind this."

Essentially, estrogen encourages the body to produce more T-cells, which, in turn, causes a stronger response, Schlesinger explained. He noted that stronger vaccine responses in women have been studied across multiple vaccines, including the flu yellow fever, and DTP shots.

"I am not at all surprised," Sabra Klein, PhD, microbiologist and immunologist at the Johns Hopkins Bloomberg School of Public Health, told The New York Times. "This sex difference is completely consistent with past reports of other vaccines." And for more on vaccine reactions, If You're Over 65, the CDC Says to Expect This After Your COVID Vaccine.

Women are also experiencing anaphylaxis more often.

A Feb. 12 study published by the Journal of the American Medical Association (JAMA) found that nearly all of the rare anaphylactic reactions to the vaccine have occurred in women. To date, all 19 of the anaphylactic reactions to Moderna had been in females, and women accounted for 44 of the 47 people who had these reactions to the Pfizer vaccine.

However, this is also nothing new. A study published by the Journal of Allergy and Clinical Immunology in 2019 found that between 1990 and 2016, women accounted for 80 percent of adult anaphylactic reactions to vaccines. And for more up-to-date information, sign up for our daily newsletter.

Experts say side effects should not deter anyone from getting the vaccine.

Doctors and scientists aren't concerned with these study results because they are consistent with past vaccines. Per Healthline, experts feel women shouldn't hesitate to get the COVID vaccine, since the potential risk of the illness is far more significant than the risk of vaccine side effects. However, women should be prepared for these side effects, so they are not caught off-guard.

"I think that there is value to preparing women that they may experience more adverse reactions," Klein told The New York Times. "That is normal and likely reflective of their immune system working." And for more vaccine advice, Dr. Fauci Just Said Don't Take This Medication With the COVID Vaccine.