Gaia Vince in The Guardian:
It was noticeable from the initial outbreak in Wuhan that Covid-19 was killing more men than women. By February, data from China, which involved 44,672 confirmed cases of the respiratory disease, revealed the death rate for men was 2.8%, compared to 1.7% among women. For past respiratory epidemics, including Sars, Mers and the 1918 Spanish flu, men were also at significantly greater risk. But why? Much of the reason for the Covid-19 disparity was put down to men’s riskier behaviours – around half of Chinese men are smokers, compared with just 3% of women, for instance. But as the coronavirus has spread globally, it’s proved deadlier to men everywhere that data exists (the UK and US notably – and questionably – do not collect sex-disaggregated data). Italy, for instance, has had a case fatality rate of 10.6% for men, versus 6% for women, whereas the sex disparity for smoking (now a known risk factor) is smaller there than China – 28% of men and 19% of women smoke. In Spain, twice as many men as women have died. Smoking, then, is unlikely to account for all of the sex disparity in Covid-19 deaths.
Age and co-morbidity (pre-existing health conditions, including diabetes, cardiovascular disease or cancer) are the biggest risk factors, and that describes more older men than women. There may also be a sex difference in how people fight infection, due to immunological or hormonal differences – oestrogen is shown to increase the antiviral response of immune cells. If women are mounting a more effective immune response to Covid-19, it could be because many of the genes that regulate the immune system are encoded on the X chromosome. Everybody gets one X chromosome at conception from their mother. However, sex is determined (for the vast majority) by the chromosome received from their father: females get an additional X, whereas males do not (they receive a Y). According to The Better Half by American physician Sharon Moalem, having this second X chromosome gives women an immunological advantage. Every cell in a woman’s body has twice the number of X chromosomes as a man’s, and so twice the number of genes that can be called upon to regulate her immune response, he says.