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A new study published on July 19 in Nature seems to have solved the mystery of asymptomatic Covid patients. These people would be carriers of a particular genetic variant and would thus be twice as likely to have no symptoms despite the infection.

If the Covid-19 has wreaked havoc on some vulnerable patients, it can be sneakier on others. Indeed, more than half of the cases are in fact asymptomatic or develop such mild symptoms that it is easy to miss an infection. Research had shown that 20% of patients had no symptoms.

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While asymptomatic patients have been the subject of numerous studies, a new research published within Nature July 19, 2023 brings a new theory that this phenomenon is due to a genetic variant.

Scientists have studied the human leukocyte antigens (HLA) of 30,000 volunteers who caught Covid-19. The researchers realized that 136 of them were asymptomatic despite not being vaccinated. One in five people in this group carried the HLA variant called “HLA-B*15:01“.

For clarification, human leukocyte antigens are cell surface molecules that allow identification by the immune system.

Some people are 8 times more likely not to get sick

People carrying the HLA-B*15:01 genetic variant would have twice as likely to be asymptomatic if they were to contract Covid-19. Patients with two copies of this genetic variant are even eight times more likely not to get sick.

To understand the link between HLA-B*15:01 and Covid, scientists looked at their T cells. The latter protect the body against their infections. They were also interested in T cells : these remember the viruses you have already encountered. They are essential killer cells in the immune response against viruses and cancers.

A cold or another coronavirus may be enough to protect

When the patients in the study first contracted Covid-19, their “HLA-B*15:01” variant T cells were more than ready to replicate because they remembered other seasonal viruses that they had previously fended off.

It would simply suffice for these people to have been exposed to another coronavirus or a common cold to be protected. A theory already suggested to understand why children tend to have fewer serious symptoms of Covid.

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