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Infectious Diseases

Updated 06 October 2020

Study sheds light on why Covid-19 hits elderly hardest

According to new research, Covid-19 patients over 80 years of age have fewer T cells than those who are younger.

  • An age-related difference in immune response may explain why older Covid-19 patients have more severe illness
  • People over 80 have fewer T cells in their blood to target virus-infected cells
  • Interfering with T cells may, therefore, be a way to control the new coronavirus and other viruses


Elderly people who get Covid-19 have lower levels of important immune cells, which may explain why they are more likely than younger patients to have severe symptoms or die, new research suggests.

For the study, the researchers analysed blood samples from 30 people with mild Covid-19, ranging in age from the mid-20s to late-90s. Compared with healthy people, all of the Covid-19 patients had lower numbers of T cells – which target virus-infected cells – in their blood.

But Covid-19 patients over 80 years of age had fewer T cells than those who were younger, and so-called "killer" T cells in older patients produced lower amounts of cytotoxic molecules that find and kill infected cells, the investigators found.

This age-related difference in immune response may partially explain why older Covid-19 patients have more severe illness, according to the authors of the study published online on 21 September in the journal mBio.

Unwelcome surprises of the pandemic

"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," said study leader Gennadiy Zelinskyy, a virologist at University Hospital Essen, in Germany.

The lower levels of T cells in Covid-19 patients is among the many unwelcome surprises of the pandemic, he noted in a news release from the American Society for Microbiology.

Once inside the body, most viruses trigger a boost in T cells, including cytotoxic-producing killer T cells that play a critical role in destroying virus-infected cells. If a person's immune system produces fewer of these T cells, it has greater difficulty combating a viral infection.

The findings suggest that cytotoxic T cells play a key role in control of early infections, but Zelinskyy said it's too soon to know if these cells can be used to create an immunotherapy against the new coronavirus.

More study is needed to understand the potential risks and benefits of interfering with T cells as a way to control the new coronavirus and other viruses, he concluded.

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