By Aara'L Yarber
Scientists have found a version of a particular gene that may explain why some people who test positive for the coronavirus never develop any Covid-19 symptoms.
The discovery could help scientists open new avenues for developing vaccines and treatments.
On average, studies have found, at least 20 percent of people who contract the SARS-CoV-2 virus are asymptomatic.
Scientists say these people might have quicker immune responses that fight the virus before symptoms can set in and lead to health complications.
"Looking at resistance allows us to basically understand how we can clear an infection," said Samira Asgari, an assistant professor of genetics and genomic sciences at the Icahn School of Medicine at Mount Sinai who was not involved in the study.
To figure out how some people manage to fend off Covid symptoms, researchers turned to human leukocyte antigen (HLA) genes, which play a critical role in our body's ability to recognise and fight pathogens.
These genetic warriors are "the most medically important region of the genome," said Jill Hollenbach, a professor in the departments of neurology and epidemiology at the University of California at San Francisco.
For their study, published on Wednesday in Nature, Hollenbach and her team enrolled 29 947 volunteer bone marrow donors, because high-quality genetic data was already available for this group.
They asked volunteers to use their smartphones daily to track their own coronavirus infections and resulting symptoms, including a runny nose, a scratchy throat, fever or chills.
Participants were also asked to record if they had taken a coronavirus test each week, and note monthly whether they had been hospitalised.
During the nine-month study period, 1 428 unvaccinated individuals reported a positive coronavirus test, and 136 of them had no symptoms.
Among the asymptomatic participants, 20 percent carried a common HLA variant called HLA-B*15:01.
People carrying two copies of this variant - one passed down from each parent - were more than eight times more likely to remain asymptomatic than those carrying other HLA variants.
The researchers also used the volunteers' data to model whether non-genetic factors affected the volunteers' chances of having an asymptomatic infection.
"There's so many things that make you more likely to have a severe disease, like various comorbidities and weight and age and sex," said Hollenbach.
"In this case, none of those things seem to be important, particularly in having an asymptomatic outcome - it seems to be mostly driven by genetics."