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It is common knowledge at this point: COVID-19 primarily kills older individuals, particularly those with health problems such cardiac and respiratory disease. However, it is puzzling that fatality rates from the virus have been significantly higher amongst men than women.
This difference first became apparent in China, when it was reported that the fatality rate in men was 2.8%, compared with 1.7% in women. This was initially put down to smoking habits: in China, around 50% of men smoke, compared to only 2% of women. Men are therefore more likely to have impaired lung and cardiac function, making them more at risk of serious complications from the virus.
As COVID-19 spread to other countries, however, data began to cast doubt on the smoking theory. In Italy, for example, 28% of men smoke compared with 19% of females, yet men still accounted for 71% of deaths.
Behavioural factors could also play a role: studies have suggested men are less likely to seek medical care, for example. However, it is difficult to see behaviour account for the size of the disparity that has been reported.
It seems, therefore, that a more fundamental mechanism is at play, perhaps rooted in the immune response. Research has suggested that the innate antiviral response in men is weaker for some viruses, though this has yet to be shown in the case of Sars-Cov-2. Many genes that regulate the immune system are found in the X chromosome, meaning that women may produce higher levels of regulatory proteins, leading to a stronger immune defence. There is also evidence to suggest that the male immune system is more susceptible to ageing, which could be particularly pertinent for a virus that primarily kills the elderly.
Sex, gender and COVID-19: Disaggregated data and health disparities: https://blogs.bmj.com/bmjgh/2020/03/24/sex-gender-and-covid-19-disaggregated-data-and-health-disparities/
Vital Surveillances: The Epidemiological Characteristics of an Outbreak of 2019 Novel Coronavirus Diseases (COVID-19) — China, 2020: http://weekly.chinacdc.cn/en/article/id/e53946e2-c6c4-41e9-9a9b-fea8db1a8f51
Men are much more likely to die from coronavirus - but why?: https://www.theguardian.com/world/2020/mar/26/men-are-much-more-likely-to-die-from-coronavirus-but-why