In a paper recently accepted in Nature, a team spanning several departments at Yale University and from Howard Hughes Medical Institute investigated differences in immune responses between men and women diagnosed with COVID-19. 

Different immune responses between males and females have been documented previously, but whether and how these immunological differences influence people's responses to COVID-19 have yet to be well-documented. Such distinctions may offer unique opportunities to better predict and monitor patient outcome and tailor therapeutic intervention. 

This team of researchers collected blood, nasal swab samples, saliva, urine, and stool from people recently admitted to the hospital who had tested positive for COVID-19. They determined the types and population sizes of specific immune cells, such as B cells, T cells, and monocytes in the samples. They also investigated the amount of molecules responsible for inflammation and cell recruitment, called cytokines and chemokines, respectively, detected in patient serum. These were compared between male and female patients as well as male and female health care workers, who served as non-infected controls. Finally, they evaluated how these factors were correlated the severity of each patient's COVID-19 symptoms.

They concluded that male patients developed lower T cell responses, specifically in a subset of T cell responsible for killing infected cells. Disease severity was greater over the course of infection in male patients who exhibited lower responses of this cell type. In female patients, disease severity was more determined by elevated inflammatory cytokines and chemokines. 

Furthermore, older males had worse disease outcomes, correlating with the less robust T cell responses in this population, while this trend did not hold true for females. 

This study provides important preliminary understandings of the difference of responses between males and females during COVID-19 infection.