Older males who have recovered from a severe attack of Covid-19 make ideal candidates for donating plasma for treating the viral infection, according to a study by researchers at Johns Hopkins Bloomberg School of Public Health.

Sex, age, and severity of the disease may be critical in identifying Covid-19 survivors who are likely to have high levels of antibodies.

The study was published in the Journal of Clinical Investigation.

This comes as many health experts recommend convalescent plasma treatment for Covid-19 patients.

Also read: Covid-19: Antibodies fade quickly in recovering patients

Study lead author Sabra Klein, Ph D, a professor in the Bloomberg School’s Department of Molecular Microbiology and Immunology said in a statement: “We propose that sex, age, and severity of the disease should be used to guide the selection of donors for convalescent plasma transfer studies.”

Variability in antibody

She added: “This is because we found that these were significant patient characteristics that not only predicted the amount of antibody but the quality of that antibody.”

For the study, the researchers examined the blood of 126 Covid-19 survivors. They found high variability in their antibody levels and their antibodies’ ability to neutralise the coronavirus, SARS-CoV-2.

Three factors were associated with stronger antibody responses: critical patients with Covid-19 who had to be hospitalised, being older, and being male.

Anti-spike proteins

The study noted that the plasma of survivors who had been hospitalised with Covid-19 had markedly more anti-spike protein antibodies and neutralised the virus more effectively. This suggested that disease severity prompts a stronger immune response.

Also read: SARS-CoV-2 can persist upto 140 days i.e. 20 weeks post-infection: Study

“We know that the magnitude of antibody responses correlates with disease severity in other infectious diseases, such as active tuberculosis,” Klein said.