Here are the reasons why women are more likely than men to report side effects from vaccines

Issues in Women

One reason could be biological gender differences.

The side effects of vaccines are normal. These side effects indicate that the immune system is working to fight the disease.

Due to the gender distribution in the vaccine doses, side effects in women have been far greater than in men following coronavirus vaccinations in Norway.

There have been 5,635 reports to the Norwegian Medicines Agency of side effects. Four thousand six hundred eighty-four of these were from women. Their report on the vaccine’s side effects can be found here (in Norwegian).

The numbers are part of a larger picture.

Researchers at the US Centers for Disease Control and Prevention (CDC) analyzed data from 13.7 million doses of vaccines and found the same thing.


Women accounted for almost 80 percent of side effects reported, even though only slightly more than 60% of those vaccinated were female.

One reason could be that side effects of the healthcare system are more common in women. However, biological differences between men and women may also be a factor.

More likely to experience severe reactions in women

According to Sabra Klein, a microbiologist, and immunologist from Johns Hopkins Bloomberg School of Public Health, about the CDC figures, “This gender gap is totally in line with previously reported from other vaccines.”

Common side effects of the Moderna or Pfizer coronavirus vaccinations

Comirnaty (BioNTech, Pfizer).

  • More than 80% felt pain at the injection site.
  • Fatigue, headaches, muscle aches, and joint pain can all be caused by fatigue. It usually passes within a few days.
  • Some people may have swollen lymph nodes lasting 7-10 days.
  • Side effects were more common after the second dose of the medication than after the first.

Moderna Vaccine

  • In the first few days following vaccination, most people experience side effects like pain and swelling at injection sites, fatigue, headaches, and nausea/vomiting.

For both vaccines:

  • These side effects are usually mild and easily tolerated by most people. However, some people experience severe discomfort for a few days.

According to the CDC’s analysis, 13.7 million coronavirus vaccines were administered in the United States. This is why women are more likely to experience severe and rare reactions.

Women accounted for 19 of the so-called anaphylactic reactions after the Moderna vaccination. 44 out of 47 people who had anaphylactic reactions after the Pfizer vaccine were women.

According to a press release by the European Medicines Agency (EMA), most people who experienced a rare blood clot problem following the AstraZeneca vaccination were under 60.

According to the EMA, however, a review did not reveal any basis for determining specific risk factors such as gender or age.

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For better or worse, a strong immune response

In recent years, gender differences in vaccine use have been more widely discussed. Researchers wrote in a 2019 article in Seminars in Immunopathology.

Researchers found that women and girls have stronger immune responses than men and more side effects following vaccinations.

Because the immune system becomes weaker with age, young people have stronger immune responses. Women’s immune systems are more resilient than those of men.

Gullveig Gredeland, an immunologist at the Department of Clinical Medicine (UiO), says that after infections, women have stronger immune responses than their male counterparts. This includes stronger antibodies as well as stronger T-cell responses.


When fighting disease, strong immune responses can be very beneficial.

Groveland stated that women could experience stronger immune responses. This means that the immune system targets things that aren’t there.

According to a review in 2020, autoimmune diseases affect more women than men.

However, there may be other biological benefits for women.

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Hormones and X chromosome

Hormones may influence how the body deals with infections. However, it is not clear if testosterone plays an additional role. It is still a very difficult question to answer,” Anne Spurkland (an immunologist and professor at said in an article on why COVID-19 seemed to kill more men than women. This gender difference is still valid.

Maybe sex chromosomes are also responsible for the differences in the immune system’s performance in men and women.

Many genes linked to the immune system can be found on the x-chromosome. The New York Times writes.

The additional x chromosome in a woman helps to eliminate genetic diseases.

“There are many genetic diseases that affect men.” Groveland says that if one chromosome is defective, the other can fix it.”