For a study published in the scientific journal Nature, researchers from Yale University set out to determine whether or not the immune response to SARS-CoV-2 was different in women than it was in men. The results, which were the first of their kind to be released, showed that, in fact, there was a difference—quite a significant one even. “Our results revealed key differences in immune responses during the disease course of SARS-CoV-2 infection in male and female patients,” the study authors wrote. One of those key differences was that female patients were found to have a far more substantial level of T cell activation than male patients during infection. In terms of immunity, T cells are the body’s second line of defense against a virus. “If you look at [your immune system] metaphorically as an army with different levels of defense, the antibodies prevent the virus from getting in. So that’s kind of like the first line of defense,” Anthony Fauci, MD, told McClatchy in a recent interview. “For those viruses that do escape and infect some cells, the T cells come in and kill the cells that are infected or block them.“ae0fcc31ae342fd3a1346ebb1f342fcb This new study found that healthy T cell response remained as such even in older women. On the contrary, men’s already inferior T cell response to COVID got even worse with age. This helps explain why doctors were seeing older men getting more seriously ill—and dying more—than women. “When [men] age, they lose their ability to stimulate T cells,” Akiko Iwasaki, PhD, an immunologist at Yale University who led the study, told The New York Times. “If you look at the ones that really failed to make T cells, they were the ones who did worse with disease.” RELATED: For more up-to-date information, sign up for our daily newsletter. The researchers admit the study has limitations, as the patient pool examined was relatively small and the average age was over 60. However, the findings are a breakthrough in the effort to understand the difference between how men and women respond to coronavirus infection. For example, Iwasaki told The Times that “the more robust T cell responses in older women could be an important clue to protection and must be explored further.” Among other things, this information could influence how vaccines are administered—some men might need multiple doses of a vaccine where a single dose may suffice for some women, for example. And for more patterns found in people infected with coronavirus, check out The 15 Most Common Conditions That COVID Survivors Share.