Researchers study why coronavirus is killing more men than women
Early in the coronavirus outbreak, hospital data from China revealed a startling disparity: COVID-19, the disease caused by the virus, was killing far more men than women.
That difference persisted in other Asian countries, such as South Korea, as well as in European countries, such as Italy. Then, it appeared in the United States.
By mid-October, the coronavirus had killed almost 17,000 more American men than women, according to data from the Centers for Disease Control and Prevention. For every 10 women claimed by the disease in the United States, 12 men have died, found an analysis by Global Health 50/50, a U.K.based initiative to advance gender equality in health care.
That disparity was one of many alarming aspects of the new virus. It bewildered those unfamiliar with the role of gender in disease.
But the specialized group of researchers who study that relationship was not surprised. It prepared an array of hypotheses. One possible culprit was male behavior. Perhaps men were more likely to be exposed to the virus due to social factors; a disproportionately male workforce, for instance, could place more men in contact with infected people. Or men’s lungs might be more vulnerable because they were more likely to smoke in the earliest countries to report the differences.
What has become more evident, 10 months into this outbreak, is that men show comparatively weaker immune responses to coronavirus infections, which may account for those added deaths.
“If you look at the data across the world, there are as many men as women that are infected. It’s just the severity of disease that is stronger in most populations in men,” Franck Mauvais-Jarvis, a Tulane University physician who studies gender differences in such diseases as diabetes. In such cases, biology can help explain why.
◆ The male immune response. Women generally have stronger immune systems, thanks to sex hormones, as well as chromosomes packed with immune-related genes. About 60 genes on the X chromosome are involved in immune function, Johns Hopkins University microbiologist Sabra Klein told the Washington Post in April. People with two X chromosomes can benefit from the double helping of some of those genes.
Akiko Iwasaki, who studies immune defenses against viruses at Yale University, wanted to see how sex differences might play out in coronavirus infections. She and her colleagues cast a proverbial net into the immune system to fish out schools of microscopic fighters.
“We did a holistic look at everything we can measure immunologically,” Iwasaki said, listing a litany of the molecules and cells that form the body’s bulwark against pathogens: “cytokines, chemokines, T cells, B cells, neutrophils. Everything that we had access to.”
In male patients, the T-cell response was weaker, the scientists found. Not only do T cells detect infected cells and kill them, they also help direct the antibody response. “It’s like a master regulator of immune response. And when you have a drop in T cells, or in their ability to become activated, you basically lose the conductor of an orchestra,” Iwasaki said.
The power of the immune system wanes as people age, regardless of sex. But what is a gentle decline for women is an abrupt dive off a cliff for men: Iwasaki’s work indicates the T-cell response of men in their 30s and 40s is equivalent to that of a woman in her 90s.
And T cells aren’t the only immune feature disproportionately impaired in men. Another paper, published in September in PLOS Biology, examined anonymous human genetic material collected along with viruses in nasal swabs.
That study found throttled defense signals in men. When a cell detects a virus, it performs the molecular equivalent of yanking the fire alarm, said one of the study’s author, Nicole Lieberman, a research scientist at the University of Washington. That alarm is manifest in genetic messengers, called RNA, which react almost immediately.
The reaction should cause cells to churn out the first lines of defense, such as interferons, immune system molecules that, as the name suggests, interfere with the virus’s ability to reproduce. Other molecules summon specialized immune cells to destroy the pathogens. “You want the fire alarm to go off for long enough that you can get the fire department there,” Lieberman said.
Lieberman and her co-authors, however, found that in men and some older populations, the fire alarm shuts off early — maybe even before the firefighters have arrived. “That, I think, is the functional consequence, potentially, of what we’re seeing here,” she said.
◆ Harmful autoantibodies. Not only is the immune system in men weaker, but in some severe cases of the coronavirus, it may hobble itself. A study of nearly 1,000 patients with life-threatening COVID-19, published last month in Science, found evidence of molecular self-sabotage. Immune system fighters were acting against the body’s defenses, like rebellious castle guards splintering their own gates. This flaw was much more prevalent in men than women.
Specifically, the researchers detected what are called autoantibodies, molecules that bind and neutralize parts of the immune system. Those neutralizers disabled a subset of defender molecules known as type-1a interferon. Simply put, having autoantibodies led to more viral replication.
◆ Men behaving differently. Beyond these biological differences, it would be simplistic to ignore how gender’s other aspects, such as behavior and social norms, may also influence the pandemic.
Broadly speaking, men may be less likely to be worried about COVID-19 than women, fitting the pattern that women generally treat health risks more seriously. Women took a more cautious approach to the disease, a recent poll found, expressing more concern they could return to workplaces safely. Women are also more likely to follow expert advice such as mask-wearing and social distancing, according to another study that included surveys and observations of pedestrians’ behavior in New York, Connecticut and New Jersey.