COVID-19: Genetics could explain why some are asymptomatic

People with a particular genetic variant are twice as likely not to get sick when they contract COVID-19indicates on Wednesday a study published in the journal Nature.

Those with two copies of this variant are even eight times more likely to be asymptomatic, according to this study.

Previous research had shown that at least 20% of the millions infected during the pandemic did not show symptoms. To understand this phenomenon, the researchers took advantage of a database of voluntary bone marrow donors in the United States.

This base included all types of human leukocyte antigen (HLA), molecules on the surface of most cells in the body, donors.

These antigens play an important role in the immune defense. They are particularly involved in the detection of foreign agents such as viruses and bacteria.

Researchers asked nearly 30,000 people on the registry to self-report their COVID-19 tests and symptoms on a mobile phone app. Within this group, more than 1,400 unvaccinated people tested positive for COVID-19 between February 2020 and the end of April 2021, according to work carried out by the PD Jill Hollenbach of the University of California.

And of those 1,400 people, 136 had no symptoms of COVID-19 for at least two weeks before and after testing positive. One in five of these asymptomatic people carried at least one copy of the HLA variant called “HLA-B*15:01”.

To find out why they weren’t showing symptoms, the team conducted separate research on their T cells, which protect the body against infection. The researchers specifically looked at how T cells remembered viruses they had previously encountered.

When people with the HLA variant were first exposed to the COVID-19 virus, their T cells were particularly primed to replicate because they remembered other seasonal viruses that they had previously fended off.

Recent exposure to the common cold and other coronavirus could thus lead to fewer COVID symptoms: this theory has already been put forward to explain why children have often been spared the worst symptoms of COVID-19.

The researchers hope that this study can open up new treatments or vaccines in the future.

They cautioned, however, that most of the study’s participants were white, which could limit its results, and that it only covered the start of the pandemic and did not include reinfections.

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