Women are reporting more side effects after receiving COVID-19 vaccines, but they tend to produce more antibodies and could enjoy longer protection than men.
A report from the US Centres for Disease Control (CDC) examined the safety data from the first 13.7 million COVID-19 vaccines given in the US and found 79.1 per cent of people reporting side effects were women.
This is less to do with the virus itself and more to do with how women are built to have stronger immune responses than men.
The new figures just about mirror a previous CDC study that found four times as many women had allergic reactions after the 2009 pandemic flu vaccine.
And it has long been known that women tend to have more reactions to vaccines for seasonal flu, hepatitis B, and the the combined measles, mumps and rubella vaccine (known as the MMRV combination vaccine).
Why do women get more side effects?
Hormones and genes are the short answer.
Oestrogen has been found to cause immune cells to produce more antibodies – and while oestrogen is produced by males and females, men produce a smaller amount.
Flip that around, and we find that testosterone, the main male sex hormone, can suppress or weaken the immune system, more so when produced in high doses.
At the very least, testosterone has a modulating effect on immunity, contrasted to oestrogen’s boosting function.
Then there’s the X chromosome to consider.
According to a 2010 article in Nature, the X-chromosome “is partly responsible for the hyper-responsiveness of the female immune system”.
Females carry two X chromosomes, while males carry an X and a Y chromosome.
Scientists believe this doubling of the X chromosome partly explains why more women have autoimmune diseases.
Because women have a more responsive immune system than men, they’re significantly more likely to have a more severe response to a vaccine, which is essentially a modified dose of a virus.
Side effects a sign the vaccine is working
Professor Catherine Bennett, is chair in Epidemiology within Deakin’s Institute for Health Transformation.
“Women are built to have a stronger immune response, and oestrogen plays a role in that,” Professor Bennett told The New Daily.
“The good side of that is women are more likely to have a strong response to the vaccine in terms of developing immunity … and that’s from a higher rate of producing antibodies … and maybe even a more sustainable reaction.”
The cost, said Professor Bennett, is you might suffer more local side effects, such as a sore and swollen lump on the arm where you had your needle – or a short period of feeling unwell with what might feel like flu symptoms.
“It’s the price you pay for having a good immune system, and probably for getting a slightly larger dose of the vaccine relative to body size,” she said.
The outcomes, on balance, for women is better.’’
At the more extreme (and rare) end, a CDC report found that all 19 people who had anaphylaxis (severe allergic reaction) after the Moderna shot were female. With the Pfizer vaccine, 44 of the 47 people who had anaphylaxis were women.
Professor Bennett said the AstraZeneca vaccine, which most Australians will get, had been found to generate milder side effects than the Pfizer vaccine.