3 Reasons for Women Reporting More Vaccine Side Effects Than Men

Why women report more Covid-19 side effects — Three Bs: Biology, Behavior, and Bias.

By early Jan 2021, almost 80% of Covid-19 vaccine side effects reported in the US came from women. This article from USA Today from April 2021, covers the possible reasons.

Here’s a graphical summary of the findings.

3 Bs: Why women report more vaccine side-effects

1. Biology

Women show greater immune response to vaccines — almost twice as much as men. Having more “ T helper cells” that activate the immune system one reason attributed to this.

Women’s immune cells having more estrogen receptors also makes the immune response, “adaptive”.

2. Behaviour

So, women are prone to higher side-effects. Are they also more inclined to report adverse effects more than men? Do men report less?

It would appear so on both counts. Women are more engaged than men in health care, per this WHO study. Women seek care more actively unlike men. Women being in charge of care for children and the family makes them more engaged than men.

3. Bias

Dosage of vaccines and meds not adjusted for women. Unlike pediatric care where dosage is adjusted by weight, men and women get the same adult dose. Trials and studies have started to include women only recently.

Women were not included in clinical trials until 30 years ago (“for their own good”). The National Institute of Health Revitalization act of 1993 in the US established new norms for clinical research equity for women and minorities. However, research for most drugs in the market pre-dates these reforms.

Combine this bias with the biological response and we get findings that suggest half the typical dose of flu vaccine is enough for women, as compared to men.


In an era when we talk about precision medicine and personalized health care delivery eloquently, it is sobering to realize that gender equity in health care is far from reality.

In case we walk away thinking that men are in better shape, sadly not so.

Historical clinical research emphasizing white males of certain types and men’s lack of engagement, puts them at a higher risk. The extent of the risk is manifest in the life expectancy gains men have not achieved, when compared to women.

That’s a story for another time.

Hari Harikrishnan

Hari Harikrishnan

Digital Business Transformer
As a digital business executive, Hari is passionate about creating and modernizing businesses by infusing data and technology in product and service portfolios. Hari has led businesses from startups to enterprise incubations to Fortune 100 business divisions.

Hari has commercialized numerous products and services in industries ranging from healthcare to high-tech to manufacturing. His career spans leadership roles in general management, product, marketing, services, and strategy.

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