Women develop a more robust T-cell immune response against the coronavirus than men do, a new study shows

• When the immune system fights the coronavirus, T cells identify and kill infected cells. Down the road, they can remember and attack the virus if it returns.
• A new study suggests that women develop a more robust T-cell response to the coronavirus than men do.
• This could be one reason men are hit harder by severe COVID-19 infections, though scientists also suspect smoking habits and underlying health issues play a role.

Men are more likely to die from COVID-19 than women.

Recent research from the UK, which examined nearly 11,000 COVID-19-related deaths, found that men are nearly twice as likely to die of the coronavirus. Data from Wuhan, China, suggests the disparity may be even more pronounced: That study showed men were 2.4 times more likely to die of the disease than women.

A study published Wednesday in the journal Nature offers a potential reason for that trend: Women seem to develop a stronger T-cell response to the virus than men do.

"We now have clear data suggesting that the immune landscape in COVID-19 patients is considerably different between the sexes and that these differences may underlie heightened disease susceptibility in men," Akiko Iwasaki, senior author of the new study, said in a press release.

T cells are a type of white blood cell that helps our immune system identify and destroy an invading virus. They can also remember and re-attack that virus should it return. According to the new research, women develop more T cells in response to the coronavirus than men do.

What's more, the strength of men's T cell responses to the virus — how many of the protective proteins they develop, and how quickly — seems to deteriorate with age. Older men with poorer T-cell responses developed more severe cases of COVID-19, the researchers behind the new study found.

The findings raise questions about whether male and female COVID-19 patients may need different treatments: Iwasaki's team recommended therapeutic interventions and vaccines to elevate T-cell immune responses in men.

Women may produce more T cells in response to the coronavirus than men

Iwasaki and her colleagues examined a cohort of 17 male and 22 female coronavirus patients admitted to Yale-New Haven Hospital between March 18 and May 9. They found that the strength of a man's T-cell responses depended on his age: Older men had poorer T-cell responses than younger men.

A women's age, on the other hand, did not affect the robustness of her T-cell response.

However, women's immune systems sometimes seemed to respond almost too aggressively. Both the male and female patients had elevated levels of cytokines — proteins produced by white blood cells to further activate the immune response — relative to healthy individuals. But the study found that when cytokine levels were elevated, women were more likely to become severely sick.

An excess of cytokines, known as a "cytokine storm," can prompt the body to attack its own healthy cells. This can lead to acute respiratory distress syndrome, the life-threatening lung injury behind many coronavirus deaths.

Men and women may need different COVID-19 treatments

Iwasaki told the the New York Times that the findings suggest "natural infection is clearly failing" to spark a proper immune response in men, which means they may need different doses of future coronavirus vaccines.

"You could imagine scenarios where a single shot of a vaccine might be sufficient in young individuals or maybe young women, while older men might need to have three shots of vaccine," Marcus Altfeld, an immunologist at the Heinrich Pette Institute in Germany who was not involved in the study, told the New York Times.

Some female patients, meanwhile, might benefit from treatments that dampen their immune responses ahead of a cytokine storm,

"Collectively, these data suggest we need different strategies to ensure that treatments and vaccines are equally effective for both women and men," Iwasaki said in a press release.

Men's smoking habits and preexisting health conditions may also play a role

Some scientists believe that behavioral factors may also make men around the world more vulnerable to severe cases of COVID-19.

A primary difference at play is that men smoke cigarettes more than women do, on average, which impacts their illness risks. The chances that smokers need intensive care and mechanical ventilation are more than double that of nonsmokers, according to the Italian National Health Institute.

In China, more than 50% of Chinese men smoke, while less than 3% of Chinese women do, according to the Chinese Center for Disease Control and Prevention. In Italy, around 7 million men smoke compared to 4.5 million women.

Men also have higher rates of preexisting health conditions that increase their risk of developing severe coronavirus cases. According to CNN, men in Italy and China have higher rates of high blood pressure than women in both countries. Chinese men are also are more likely to have Type 2 diabetes than Chinese women.

Men also have a higher risk of coronary heart disease than women, according to the British Medical Journal.

"We see in general that there's just a higher rate of severe disease among men," Megan Coffee, an infectious disease clinician in New York City, previously told Business Insider. "Women can certainly develop acute respiratory distress syndrome, but there's a predilection towards men developing a severe outcome."

Aria Bendix contributed reporting to this story.