Scientists are looking into why some people avoid COVID-19.

Most people in the U.S. have had COVID-19 at least once—probably more than 70% of the country. White House COVID-19 Response Coordinator Ashish Jha said Thursday, citing data from the Centers for Disease Control and Prevention.

Many people are affected multiple times. In a ___ Preprint study looking at 257,000 US veterans Among those who had contracted COVID-19 at least once, 12% had been re-infected by April and about 1% had been infected three times or more.

This raises an obvious question: What is keeping this shrinking minority from getting sick?

Epidemiologists are focusing on a number of predisposing factors beyond individual behavior, including genetics, T-cell immunity and the effects of inflammatory conditions such as allergies and asthma.

But even as experts learn more about the reasons why people may be better equipped to survive COVID-19, they warn that some of these defenses may be limited by Omicron’s latest version, BA. Can’t be against .5, which is great at spreading and avoiding. Vaccine safety.

“It really takes two to tango,” said Neville Sanjana, a bioengineer at the New York Genome Center. “If you think about an infection and anything bad that follows, it’s really the product of two different organisms: the virus and the human.”

Genetics may reduce risk of COVID-19.

In 2020, researchers at New York University identified a large number of genes. which can affect a person’s susceptibility to the coronavirus. Specifically, they found that blocking certain genes that code for a receptor known as ACE2, which allows the virus to enter cells, can reduce a person’s chance of infection.

Sanjana, who conducted the research, estimated that about 100 to 500 genes may influence susceptibility to COVID-19 in sites such as the lungs or nasal cavity.

Genetics is likely to be a “huge contributor” to protection against COVID-19, he said. “I would never say it’s the only contributor.”

In July, researchers identified a common genetic factor that may influence the severity of a coronavirus infection. In a ___ the study Among more than 3,000 people, two genetic mutations reduced the expression of a gene called OAS1, which is part of the innate immune response to viral infections. This was associated with an increased risk of COVID-19 hospitalization.

Then, increasing gene expression should have the opposite effect – reducing the risk of severe disease – although it would not necessarily prevent infection entirely.

“It’s very natural to have an infection once you’re exposed. There’s no magic bullet for that. But once you’re infected, how you respond to that infection is affected by your genetic mutation. It is,” said Lyudmila Prokonina-Olson, the study’s principal investigator and chief of the Laboratory of Translational Genomics. National Cancer Institute.

Still, Benjamin Tenover, a professor of microbiology at the NYU Grossman School of Medicine who helped with the 2020 study, said it would be difficult for scientists to pinpoint a specific gene responsible for preventing COVID-19 infection. .

“Although there are certainly still some genetics out there that make people completely resistant, it’s going to be incredibly difficult to find them,” tenOever said. “People have already been watching intensely for two years without any real results.”

Photo: A Person Takes A Covid-19 Test Outside The Salt Lake County Health Department On July 22, 2022.  (Rick Boomer/Ap)

Photo: A person takes a Covid-19 test outside the Salt Lake County Health Department on July 22, 2022. (Rick Boomer/AP)

T cells can remember past coronavirus encounters.

In addition to this new coronavirus, SARS-CoV-2, four other coronaviruses commonly infect people, usually causing mild to moderate upper respiratory illnesses similar to the common cold.

Oh A recent study suggested that exposure to repeated or occasional infections with these common cold coronaviruses may confer some protection against SARS-CoV-2.

The researchers found that T-cells, a type of white blood cell that recognizes and fights invaders, seem to recognize SARS-CoV-2 based on past exposure to other coronaviruses. So when someone who has been infected with the common cold later contracts SARS-CoV-2, they may not be as sick.

But that T-cell memory may not completely prevent COVID-19.

“While neutralizing antibodies are key to preventing infection, T cells are essential for eliminating infection and reducing the severity of infection,” said study author and La Jolla Institute for Immunology professor Alessandro Sette. are key.”

Sett said it’s possible that some people’s T cells clear the virus so quickly that the person never tests positive for COVID-19. But researchers still aren’t sure what’s going on.

“It’s possible that, despite the negative test, it was a very latent, transient infection that went undetected,” Sett said.

At the very least, he said, T cells from past COVID-19 infections or vaccines should continue to provide some protection against coronavirus variants, including BA.5.

Allergies may result in a little extra protection.

Although asthma was previously considered a potential risk factor for severe COVID-19 in the pandemic, recent research suggests that low-level inflammation from conditions such as allergies or asthma may have a protective benefit.

“You’ll hear stories of some people getting sick and having full-on symptoms of COVID, and during that period they’ve had their partner without sleeping for a whole week. People think they have some genetic predisposition against it. There is resistance, of course. [but] A big part of that could be if their partner somehow has an over-the-top inflammatory response in their lungs,” tenOever said.

Oh can study It found that having a food allergy halved the risk of coronavirus infection in about 1,400 American households. Asthma did not reduce people’s risk of infection in the study, but it did not increase it either.

One theory, according to the researchers, is that people with food allergies express fewer ACE2 receptors on the surface of their airway cells, making it harder for viruses to enter.

“Because there are fewer receptors, you’re either going to have a much lower level of infection or you’re less likely to get an infection,” said Tina Hart, M.D., professor of medicine and pediatrics at Vanderbilt University School of Medicine. research

The study took place from May 2020 to February 2021, before the Omicron variant was introduced. But Hartert said BA.5 likely won’t eliminate cross-protection from allergies.

“If something like allergic inflammation is protective, I think that would be true for all types,” Hartert said. “The extent to which it can be protective can certainly vary.”

Infection with BA.5 is more difficult to avoid.

For many people, the first explanation that comes to mind when thinking about how to avoid COVID-19 is one’s personal level of precaution. NYU’s TenOever believes that individual behavior, more than genetics or T-cells, is the key factor. He and his family are among the few people in New York City who have never contracted COVID-19, which he attributes to precautions such as staying at home and wearing masks.

“I don’t think for a second that there’s anything specific in our genetics that makes us resistant,” he said.

It is now common knowledge that it was easy to prevent COVID-19 before omicron, when a small percentage of infected people were responsible for the majority of the virus’s spread. Oh 2020 studyFor example, 10% to 20% of infected individuals have been found to have 80% of transmissions.

But omicron and its subtypes have made any social interaction dangerous for everyone involved.

“It’s probably a more level playing field with the Omicron variants than it was for the earlier variants,” Tenover said.

BA.5, in particular, has increased the odds that people who have so far avoided COVID-19 will become ill. President Joe Biden is a prime example: He tested positive for the first time this week.

But even so, Jha. said on Thursday In a news briefing, “I don’t believe every American will be affected.”

This article was originally published by NBC News.