Scientists are narrowing down why some people continue to avoid Covid.  BA.5 can end this luck.

Scientists are narrowing down why some people continue to avoid Covid. BA.5 can end this luck.

The majority of people in the United States have had Covid-19 at least once — likely more than 70% of the country, Ashish Jha, the White House’s Covid-19 response coordinator, said Thursday, citing data from the Centers for Disease Control and Prevention.

Many were injured multiple times. In a preprint study that looked at 257,000 US veterans who had had Covid at least once, 12% had been infected again by April and about 1% had been infected three or more times.

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

Pathologists target certain predictive 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 are more willing to avoid Covid, they warn that some of those defenses may not hold up against the latest omicron version, BA.5, which is remarkably good at spreading and avoiding vaccine protection.

“Tango really takes two people,” said Neville Sanjana, a bioengineer at the Genome Center in New York. “If you think about getting an infection and any of the bad things that happen after that, it’s really the product of two different organisms: the virus and the human.”

Genetics can reduce the risk of contracting Covid

In 2020, New York University researchers identified a large number of genes that can influence a person’s susceptibility to infection with the coronavirus. In particular, they found that inhibiting 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 this research, estimated that around 100 to 500 genes could influence susceptibility to Covid-19 in sites such as the lungs or nasal cavity.

He said genetics was “likely to be a significant contributor” to protection against Covid-19. “I wouldn’t say he’s the only shareholder.”

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

Thus, increasing the expression of the gene should have the opposite effect – reducing the risk of developing severe disease – although it will not necessarily prevent infection completely.

“It’s very normal to get infected once you’re exposed. There’s no magic bullet for that. But after you get infected, how you’re going to respond to that infection, that’s what will be affected by your genetic variants,” Ludmila Prokunina-Olsson, the study’s lead researcher and head of the Transitional Genomics Laboratory at National Cancer Institute.

However, Benjamin Tenover, a professor of microbiology at New York University’s Grossman School of Medicine who helped conduct the 2020 research, said it would be difficult for scientists to identify a specific gene responsible for preventing infection with the Covid virus.

“While there are certainly some genes that make people quite resistant, they are going to be very difficult to find,” TenOever said. “People have already searched extensively for two years with no actual results.”

T cells can remember previous coronavirus encounters

Aside from this new coronavirus, SARS-CoV-2, four other coronaviruses commonly infect people, usually causing mild to moderate upper respiratory illnesses such as the common cold.

A recent study suggests that repeated exposure or accidental infection from 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, appear to recognize SARS-CoV-2 based on previous exposure to other coronaviruses. So when a person infected with the coronavirus is later exposed to SARS-CoV-2, they may not get sick.

But this memory of T cells may not be able to prevent Covid completely.

“While neutralizing antibodies is key to preventing infection, T cells are key to terminating infection and modulating the severity of infection,” said Alessandro Seit, study author and professor at the La Jolla Institute of Immunology.

It’s possible for some people’s T cells to get rid of the virus so quickly that a person would never have had Covid, Seit said. But researchers aren’t sure yet if that’s what’s happening.

“It is possible that despite the negative results in the test, it was a failed, transient infection that went undetected,” Set said.

At a minimum, he said, T cells from previous Covid 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 considered a potential risk factor for severe COVID-19 early in the epidemic, recent research suggests that low-grade inflammation from conditions such as allergies or asthma may have a protective benefit.

“You’ll hear these stories about some individuals who got sick and had full symptoms of Covid, and slept next to their partner for an entire week during that time without giving them that. People think they must have some genetic resistance ceiling, [but] A big part of that could be if the partner next to them in any way has a higher-than-normal inflammatory response going on in their lungs,” Tenover said.

A May study found that having a food allergy cuts the risk of contracting the coronavirus in half among nearly 1,400 American families. Asthma did not reduce the risk of infection for the people in the study, but it did not raise it either.

One theory, according to the researchers, is that people with food allergies show fewer ACE2 receptors on the surface of their airway cells, making it more difficult for the virus to get in.

said Tina Hartert, MD, professor of medicine and pediatrics at Vanderbilt University School of Medicine, who co-led the research.

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

“If there was such a thing as allergic inflammation as preventive, I think it would be true for all the variables,” Hart said. “The degree to which it can be protective can certainly vary.”

Avoiding infection is more difficult with BA.5

For many, the first explanation that comes to mind when thinking about avoiding Covid is a personal level of caution. TenOever of New York University believes that individual behavior, more than genes or T cells, is the key factor. He and his family in New York City are among those who have never had Covid, which he credits with precautions such as staying home and wearing masks.

“I don’t think for a moment that we have anything special in our genetics that makes us resist,” he said.

It is now known that Covid was easier to avoid before omicron, when a small percentage of infected people were responsible for the majority of the virus’ spread. A 2020 study, for example, found that 10% to 20% of infected people account for 80% of transmission cases.

But Omicron and its sub-variables made any social interaction more risky for everyone involved.

“It’s probably a much more level playing field with omicron variants than it has ever been for previous variants,” TenOever said.

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

But nevertheless, Jha said at a news briefing Thursday, “I don’t think every American is going to get infected.”

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