A new study published in mBio , an open-access journal of the American Society for Microbiology, puts forth the reason why older people tend to suffer severe outcomes of the coronavirus.

According to the study, older people have a low frequency of immune responses that are needed to destroy the virus in the body.

Lead author and virologist Gennadiy Zelinskyy, at the University Hospital Essen, in Germany, said in a statement: “Elderly people have more severe diseases compared to young people, and we found that the cytotoxic part of immune control is not as efficient to respond to the virus in older people.”

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For the study, Zelinskyy and his team examined blood samples from 30 mild cases of Covid-19 to observe how killer T cells, which are necessary to eliminate the virus from the body, respond to the novel coronavirus.

Researchers found that coronavirus causes the depletion of T cells in the blood of the patients. This reduction has been one of many unwelcome surprises from Covid-19, said Zelinskyy.

How does this work?

When foreign agents enter the body and infect the host’s cells, the immune system responds to them by activating and expanding the T cells’ response. These cells in turn produce cytokine storms to destroy the foreign agents completely.

However, if a person’s immune system produces fewer of these T cells, said Zelinskyy, it will be less successful at fighting off a viral infection.

The researchers similarly noted in their study that the number of CD8+ T cells producing cytotoxic molecules in response to virus diminished with increased age, and that reduction was significantly higher, on average, in patients over 80.

Moreover, the “killer” T cells from patients aged 80-96 produced cytotoxic molecules at a lower frequency than similar cells from younger patients, the study added.

“Cytotoxic T cells really fight for control during this acute phase of infection,” Zelinsky said.

Also read: Why Covid-19 could be life-threatening for some patients

If an elderly patient’s immune system produces fewer killer T cells, and these cells are inadequately armed then they may be mounting an insufficient defense against SARS-CoV-2. The viral particles can continue to spread and, as a result, the infection worsens, he explained in his research.

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