One of the mysteries of the new coronavirus is that it is deadlier for men than women.
As of April 7, 2,232 men had died of COVID-19 in New York City — the epicenter of infections in the U.S. — compared to 1,309 women, according to the city's health department.
When it came to hospitalizations, there were more than 40,000 male patients, compared to about 34,000 female patients. The COVID-19 death rate per 100,000 people in New York City stood at 55 for men and less than 30 for women.
Men seem to be getting the disease more often and they seem to be having worse outcomes from it, said NBC News medical correspondent Dr. John Torres.
"It is true that men seem to be suffering more seriously," Torres noted.
White House coronavirus coordinator Dr. Deborah Birx previously pointed out this “concerning trend” after looking at statistics in Italy, where footage of hospital intensive care units showed bed after bed of older men breathing with the help of ventilators.
“The mortality in males seems to be twice in every age group of females. This should alert all of us to continue our vigilance to protect our Americans that are in nursing homes,” Birx said March 20 during a briefing of the Trump administration's coronavirus task force.
When Italy recently reported the country’s death toll, 72% of those who had died were men, according to the BBC. One study put the number even higher, with men making up 80% of people who had passed away in Italy.
Experts have suggested a number of factors that may help explain the disparity, including immune system differences between men and women, the protective effect of estrogen, lifestyle habits and the tendency for men to have more risk factors.
For example, men are more likely to smoke — with 40% of men smoking cigarettes worldwide compared to 9% of women, according to the World Health Organization — which puts them at higher risk of lung disease and a tougher battle when a respiratory virus strikes.
Men also drink more alcohol and may put off going to a doctor when feeling unwell.
Meanwhile, women may have the edge when fighting a viral infection.
“There’s something about the immune system in females that is more exuberant,” Dr. Janine Clayton, director of the Office of Research on Women’s Health at the National Institutes of Health, told The New York Times.
Women mount higher innate and adaptive immune responses than men, which can result in "faster clearance of viruses,” one study found.
They also may have an immune advantage from having two X chromosomes, which “could contribute to an immunological advantage for females in many infections,” according to another paper.
Still, the full explanation remains elusive as the coronavirus outbreak grows.