One aspect of the coronavirus pandemic which is baffling scientists is why it affects certain groups more than others. So for instance, why does coronavirus hit men harder than women?
While men and women seem to be equally likely to contract coronavirus, more men end up in intensive care and subsequently die from coronavirus COVID-19 than women. But why? Is it a physiological, behavioural or cultural issue?
It’s well known that men tend to die younger than women and are more prone to life-threatening ailments such as heart disease and cancer. Previous coronavirus epidemics, such as SARS, seems to have affected men worse than women, and so far the situation seems to be the same for COVID-19.
Six countries have published death statistics sorted by gender, and in all of them, the death rate is higher for men than for women – in four of them, China, France, Italy and South Korea, more than 50 percent higher.
In England, Wales and Northern Ireland around 70 per cent of critically ill patients admitted to intensive care have been male, and a higher proportion of men than women have died. A study of more than 4000 COVID-19 patients in New York City hospitals found that 62 per cent were male.
Of course these statistics are subject to all sorts of possible errors, but they do point to an undeniable trend.
So why does it seem that men are being hit harder than women? Could it be a biological difference, or is it due to the way men behave?
One factor may be that coronavirus is particularly dangerous for people with underlying health issues, and men do tend to be more affected with cardiovascular or pulmonary issues or high blood pressure. In part this is due to lifestyle issues such as smoking and drinking.
But there could be other factors at work, such as willingness to comply with social isolation and hygiene issues – could it just be that men are less inclined to wash their hands properly, or stay at home? Certainly statistics show that they are less likely to use health services.
But there is another possible explanation, a biological one to do with the immune system. Sex hormones which differ in men and women are involved in triggering the response of the immune system to pathogens, and women’s immune systems seem to be more responsive.
“There are substantial differences in the immune system between males and females and these have significant impact on outcome from a wide range of infectious diseases,” says immunologist Philip Goulder at the University of Oxford.
The suggestion is that women have two X chromosomes per cell whereas men have only one one, and a number of critical immune genes are located on the X chromosome, in particular the gene for a protein called TLR7, which detects single-stranded RNA viruses like the coronavirus. “As a result, this protein is expressed at twice the dose on many immune cells in females compared to males, and the immune response to coronavirus is therefore amplified in females,” says Philip Goulder.
Other researchers have suggested that the female sex hormones oestrogen and progesterone boost the immune system, though this hasn’t yet been specifically investigated in COVID-19.
There’s even a theory that viruses have evolved in this way because women are more valuable as hosts. Francisco Úbeda and Vincent Jansen at Royal Holloway University of London suggest that women can pass infections to their children during pregnancy, birth and breastfeeding, so there’s an evolutionary pressure on viruses to be less harmful to them.
So why does coronavirus hit men harder than women, and can anything be done about it? Researchers may not have the full answers until years of analysis have been completed.