A late immune response may explain why COVID-19 often hit harder and cause more deaths among men and people over 65, according A study published this Tuesday in the magazine PLOS Biology.

Researchers Nicole Lieberman and Alexander Greninger of the University of Washington School of Medicine concluded in their study that differences by age and sex on the impact of the disease caused by the new coronavirus can depend on viral load and time course of infection.

“Our data show that individual responses to SARS-CoV-2 depend on viral load and time the infection takes, with differences observed due to age and sex that could contribute to the severity of the disease, “the study authors noted.

Researchers extracted and sequenced genetic material Viral (RNA) from swabs collected from 430 people who tested positive for COVID-19 and 54 who tested negative, as a control, and analyzed their immune and antiviral responses based on infection status, viral load, age and sex .

Their conclusion was that cellular immune responses generally did not activate until about three days later infection began, and that the strength of that reaction fluctuated based on viral load.

Fewer key agents in the immune system

Compared with younger patients, older patients tended to have “reduced expression” of key agents in the immune system, which could have led to “deficiencies” in T-cell activity and “natural killer cells” (NK), decisive to mount a good defense against pathogens.

In addition, compared to women, men appeared to show reductions in the activity of NK and B cells, another type of immune agent, the experts noted.

Scientists warned that still more studies are needed to confirm their finding, because the samples that were taken for their study came from the nasopharyngeal area, “which is not a sensitive anatomical location to precisely examine the signs of systemic inflammation.”