Researchers are still not entirely sure why this is. But there are already some intriguing clues.
Could it be higher rates of smoking among men? A higher likelihood of delaying medical care? Or do the answers lie among the genes and sex hormones in our bodies that are setting men on a riskier course if they encounter the virus?
As Marcia Stefanick, a professor of medicine at Stanford University School of Medicine, told the Wall Street Journal, “There are profound sex differences in immune systems, and this pandemic is revealing them.” But, she noted, “What is biology versus what are our social norms and gender behaviors confounds our ability to understand what’s going on.”
Finding answers could help develop more effective treatment protocols and prevention measures, as well as lead to a more successful vaccine.
Biological forces at play
One key piece of context for these questions is that there are, in general, a variety of key biological differences in the way men and women fight off infections. Women, for example, tend to mount a stronger immune response. Researchers think this is in part because most women have two X chromosomes, and the X chromosome happens to contain most of the genes related to the immune system (and those with two X chromosomes instead of one also have a wider diversity of immune responses). This extra immune functioning, however, also seems to put women more at risk for autoimmune diseases, such as rheumatoid arthritis and Crohn’s disease.
Hormones might also help provide women with a more effective defense. Some important immune cells have estrogen receptors, and an estrogen supplement has been shown to increase general immune responses in mice.
A 2017 study in the Journal of Immunology specifically looked into sex differences from the coronavirus that causes SARS (which seems to have killed more men than women during an outbreak in 2003). In that study, researchers found that male mice were more susceptible to the virus. But when they blocked estrogen from working normally in the female mice, the females fell ill at higher rates.
Women might also be more likely to launch an earlier attack on infections in general, saving the body from needing to use all of its virus-fighting might later — an event that can skyrocket inflammation and often do more damage to key organs.
These sex patterns are not universal among infections. And data from other viruses, including influenza, sometimes even skews in the other direction, with more women dying than men. There’s still a lot to learn about the novel coronavirus, and so far there aren’t any studies on it looking specifically at these biological factors. We don’t yet know how these biological differences play out for Covid-19, if they do at all. But they’re definitely possibilities.
Behavioral factors could also be involved
There are also clues that differences in behavior could be putting men at higher risk for severe Covid-19. It can be a difficult (and time-consuming) endeavor for epidemiologists to untangle behavioral risk factors from one another, so it’s important to remember that at this point, what we have are correlations that suggest possible risks, not hard proof.
One factor could be smoking rates. A review of existing research as of March 17 concluded that “smoking is most likely associated with the negative progression and adverse outcomes of Covid-19.” There are a couple of reasons this could be the case, the World Health Organization notes. One is that smokers are more likely to have lung disease, which is an established risk factor for severe infection. The other is that when smoking, a person is more likely to touch their mouth or face, possibly allowing the virus an easy path in.
And smoking is often more common among men than women. According to a 2017 analysis in the Journal of Epidemiology & Community Health, 54 percent of Chinese adult men smoked tobacco, compared with just 2.6 percent of Chinese women. The World Bank reports that, as of 2016, about 41 percent of South Korean men smoked versus about 6 percent of women. (Spain also shows the same general trend, as does the US, but the sex difference isn’t as large as it is for China and South Korea.)
Because the research on all of this is so new, it will still probably be some time before we have a clear understanding of what role smoking might play.
Other broad social and cultural variations among genders (that, to be sure, are not universal) might be further exacerbating this trend. For example, in the US, various studies show that men wash their hands less often and are less likely to seek care earlier in an illness. A March 24 poll from Reuters revealed that a smaller percentage of men than women were taking warnings about the coronavirus seriously — including changing their behavior.