The coronavirus may infect anyone, young or old, but older men are up to twice as likely to become severely sick and to die as women of the same age.

Why? The first study to look at immune response by sex has turned up a clue: Men produce a weaker immune response to the virus than do women, the researchers concluded. The findings, published in Nature, suggest that men, particularly those over age 60, may need to depend more on vaccines to protect against the infection.

“Natural infection is clearly failing” to spark adequate immune responses in men, said Akiko Iwasaki, an immunologist at Yale University who led the work.

The results are consistent with what’s known about sex differences following various challenges to the immune system. Women mount faster and stronger immune responses, perhaps because their bodies are rigged to fight pathogens that threaten unborn or newborn children.

But over time, an immune system in a constant state of high alert can be harmful. Most autoimmune diseases — characterised by an overly strong immune response — are much more prevalent in women than in men, for example. “We are looking at two sides of the same coin,” said Dr. Marcus Altfeld, an immunologist at the Heinrich Pette Institute and at the University Medical Center Hamburg-Eppendorf in Germany.

The findings underscore the need for companies pursing coronavirus vaccines to parse their data by sex and may influence decisions about dosing, Dr Altfeld and other experts said. “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,” Dr Altfeld said.

Dr Iwasaki’s team analysed immune responses in 17 men and 22 women who were admitted to the hospital soon after they were infected with the coronavirus.

Over all, the scientists found, the women’s bodies produced more so-called T cells, which can kill virus-infected cells and stop the infection from spreading.

Men showed much weaker activation of T cells, and that lag was linked to how sick the men became. The older the men, the weaker their T cell responses. “When they age, they lose their ability to stimulate T cells,” Dr Iwasaki said. “If you look at the ones that really failed to make T cells, they were the ones who did worse with disease.”

New York Times News Service