Women are much more likely than men to report side-effects after a Covid-19 vaccine, new figures from the French medicine safety agency have shown. We explore why
In its latest figures and update on March 19, the Agence nationale de sécurité du médicament et des produits de santé (ANSM) found that there had been 14,402 reports of unwanted side-effects after a Covid-19 vaccine, of the 6,762,000 people who had received at least one vaccine dose to that date in France.
This represents less than 1% (0.2%) of people vaccinated.
Yet, ANSM has also seen that between 74.4-79.9% (depending on the vaccine) of the people to have reported side-effects were women.
These figures align with those from US health authority the Centers for Disease Control (CDC), which has also said that 77-78% of people reporting unwanted, non-severe side-effects after having received the Pfizer or Moderna vaccines were women.
This does not necessarily mean that women are simply biologically more likely to get side-effects, however. We explain.
More women have been vaccinated
Health authorities have said that one possible explanation for the figure could be that proportionally more women have been vaccinated than men in France.
This is partly due to the vaccination campaign having started by prioritising older people and healthcare workers and nurses; of which more are women than men.
Figures from French statistics institute Institut national de la statistique et des études économiques (Insee) show that there are 5,890,000 women aged 70 or over in France, compared to 4,210,000 men. Similarly, women make up 86.6% of nurses.
Yet, the demographics do not fully explain why women have reported more side-effects than men.
Women make up 60% of the people to have received two doses, but this is much less than the 79.9% of side-effects reported by women.
Women react to vaccines more than men in general
Studies have shown that women produce more antibodies in response to vaccines than men. This phenomenon has been seen across vaccines against flu, yellow fever, MMR, rabies, and hepatitis.
Studies in the US from 2013, during a flu vaccination campaign, showed that women aged 20-59 were four times’ more likely to develop allergic reactions to the vaccine than men were. Another study in the US, published in 2019, showed that between 1990-2016, 80% of anaphylactic reactions to vaccines were in women.
According to studies by Professor Sabra Klein, a microbiologist and immunologist at the Johns Hopkins Bloomberg School of Public Health in Maryland, US, these side-effects generally tend to show up as “fatigue, pain or swelling of the arm [that was injected], headaches, and maybe a light fever”.
Yet, Professor Klein has also said that getting mild side-effects after a vaccination are not negative, but in fact a positive sign.
She wrote: “These physical reactions are a sign that the vaccine is working and that you are developing a very strong immune response, and you will probably be protected as a result.”
The dosage amounts of the vaccines are not adapted to women
Some have suggested that the dosage amount in each vaccination could be a reason that women react more, as they are getting proportionally “more” of the doses than a man would.
Professor Klein said: “In adults, the vaccine doses are one-size-fits-all, whatever your size or biology. I think that there are reasons to study, and try to understand, if women could be protected with a smaller dose of the vaccine.
“Too often, vaccine manufacturers use a one-size-fits-all approach, because it’s easier to administer.”
One study from 2004-2005 gave “half doses” of the flu vaccine to women, and full doses to men. It showed that women responded in the same way as men, even though they received lesser doses. Further studies have also shown that women absorb and metabolise medicines differently to men.
Women are more likely to report health issues than men
Doctors have also said that women are generally more likely to admit to having side-effects than men, due to societal expectations.
Professor Klein said: “It is maybe a little more socially acceptable for women to feel pain, to say that they don’t feel well, or that they are injured. In many cultures and societies, men [feel as though they] have to be strong and not say if they don’t feel well or something hurts.
“I think that these cultural factors can absolutely contribute.”
No specific research has been done in relation to the vaccine and this suggestion, but one study has shown that men are less likely than women to go to a doctor when they are ill.