Why Are Women Reporting More Vaccine Side Effects?

Why Are Women Reporting More Vaccine Side Effects?

What would be a not-ideal scenario for someone who struggles for 3 weeks to get over the common cold? A new respiratory virus that spreads exponentially across the globe.

Like millions of other Americans, I spent much of the last year in social isolation awaiting the development and distribution of a vaccine. After the FDA began approving COVID-19 vaccines for emergency use, I spent some time researching the reactogenicity information of the approved vaccines.1-3 What we call symptoms or adverse side effects of a vaccine are essentially the physical evidence of our inflammatory response to vaccination (or, reactogenicity).4 As the CDC data indicates, people react differently to vaccines; some people will experience side effects and others will not.

I suspected I would experience minor – if any – effects from the first dose of my mRNA vaccine. I was mostly right. And, let me be perfectly honest… I was willing to put up with a lot more than the mild headache I experienced. After all, the last 13 months have been a whirlwind of health, economic, and social costs that spared no one, not even my own family.

As the countdown to my second dose closed in, I started to prepare myself for potentially feeling worse than the first time around. According to the available data on reactogenicity, some of the most common side effects for people my age receiving their second dose of an mRNA vaccine include pain at the injection site, fatigue, headache, muscle pain, chills, joint pain, and fever.1-2

I woke up the day after my second dose with a stabbing pain at the base of my neck that continued down to the middle of my back. Moving my head in any direction resulted in excruciating pain, and this continued for several days. Of course, I am exceptionally happy and thankful to be fully vaccinated. Sharing my experience does not diminish my appreciation for the vaccine. Instead, being open and transparent about potential adverse effects perhaps normalizes the experience for others. For myself, preparation and knowledge help: I am far less anxious when experiencing an expected health-related issue, like pain after a vaccination. Uncertainty, on the other hand, is the foundation of fear.

According to a study published last month, side effects from multiple COVID-19 vaccines were significantly more prevalent in women than in men5. While our COVID-19 vaccines are new, women’s higher prevalence of adverse side effects after receiving vaccinations is not. When analyzing data for the 2009 flu vaccine, scientists noted that women between the ages of 20 and 59 reported four times as many allergic reactions than men.6

Talking about sex or gender differences in health is complex because both biological and social factors may be involved. Across the globe, women tend to have longer life expectancies than men, but they also have higher morbidity rates. Men and women are both susceptible to autoimmune disorders, but the prevalence of autoimmune disorders is much higher in women. Scientists have noted that there are marked differences between men and women in their immune responses after vaccinations, and women tend to experience more robust immune responses.7 This indicates that we should not be completely surprised that women are reporting more side effects after receiving COVID-19 vaccinations. The reasons exactly why are still being explored, but they may be related to sex hormones, chromosome (dis)advantage, and other factors.

There is also a social aspect involved in reporting vaccine side effects. Some news articles have put forth the idea that women are more willing to report feeling ill, which may contribute to their higher reporting of vaccine side effects. Health-seeking studies have shown that men are more likely to delay seeking healthcare when feeling ill, and sometimes this is tied to ideas about masculinity.8 However, this has not yet been studied in relation to COVID-19 vaccines, so it’s an area ripe for exploration by scientists.

So, why should we care that women report more adverse side effects than men?

There is value in medical transparency. Women should be informed that they are more likely to experience side effects from vaccines, but this should be worded in a way that highlights both the mild magnitude of most side effects and the normalcy of feeling slightly unwell after vaccination. Perhaps this discussion could lead to additional research and breakthroughs on immune responses by gender. If so, scientists could also investigate whether improvements to the vaccination experience for women could exist in the future. This is important, as some women have stopped receiving flu vaccinations due to reported discomfort from reactions.9

In addition to medical transparency, there are additional reasons women should know that they may be at higher risk of experiencing side effects. While most side effects are mild, others might have a more notable impact on day-to-day functioning immediately after the vaccine. This has relevancy in both the home and workplace.

Women have historically engaged in more child-related caretaking responsibilities within the home, and this has continued during the COVID-19 pandemic – even when both parents still work.10 If women are informed in advance that they may feel unwell after vaccination, some women may be able to stagger their vaccines such that their spouse, partner, or another household member could assist with childcare if needed. In the workplace, employers should prepare that women may be more likely to report feeling unwell and potentially miss work; this is particularly relevant in workplaces that require temperature checks or other symptom monitoring before entering. Depending on the company policy, women may be required to miss work if they show visible symptoms (e.g. fever), even if they believe all symptoms are vaccine related.

Vaccines are likely to continue being part of the public health response to future pandemics and viruses. Sharing our own incidents, or lack thereof, allows us to connect our lived experience to the bigger scientific picture, which is pretty neat! Ideally, open communication will build broader trust in science and medicine rather than a hesitancy towards a vaccine.



1.     https://www.cdc.gov/vaccines/covid-19/info-by-product/moderna/reactogenicity.html

2.     https://www.cdc.gov/vaccines/covid-19/info-by-product/pfizer/reactogenicity.html

3.     https://www.cdc.gov/vaccines/covid-19/info-by-product/janssen/reactogenicity.html

4.     Hervé, C., Laupèze, B., Del Giudice, G. et al. The how’s and what’s of vaccine reactogenicity. NPJ Vaccines. 2019;4:39. doi: 10.1038/s41541-019-0132-6. eCollection 2019.

5.     Menni, CM., Klaser, K, May, A, et al. Vaccine side-effects and SARS-CoV-2 infection after vaccination in users of the COVID Symptom Study app in the UK: a prospective observational study. Lancet Infect Dis. 2021;S1473-3099(21)00224-3. doi: 10.1016/S1473-3099(21)00224-3. Online ahead of print.

6.     Halsey, NA., Griffioen, M., Dreskin, SC., et al. Immediate hypersensitivity reactions following monovalent 2009 pandemic influenza A (H1N1) vaccines: Reports to VAERS. Vaccine. 2013;31(51):6107-6112. doi: 0.1016/j.vaccine.2013.09.066

7.     Furman, D., Hejblum, BP., Simon, N., et al. Systems analysis of sex differences reveals an immunosuppressive role for testosterone in the response to influenza vaccination. PNAS. 2014;111(2):869-874. https://doi.org/10.1073/pnas.1321060111

8.     Galdas, PM., Cheater, F., Marshall, P. Men and health help-seeking behaviour: literature review. J Adv Nurs. 2005;49(6):616-23. doi: 10.1111/j.1365-2648.2004.03331.x.

9.     Chang, WH. A review of vaccine effects on women in light of the COVID-19 pandemic. Taiwan J Obstet Gynecol. 2020;59(6):812-820. doi: 10.1016/j.tjog.2020.09.006

10.  Zamarro, G., Prados, MJ. Gender differences in couples’ division of childcare, work and mental health during COVID-19. Rev Econ Household. 2021;19:11-40. https://doi.org/10.1007/s11150-020-09534-7

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Kara Fransisco

Kara Fransisco