By Aria Bendix —
NBC News
Most people in the US have had COVID-19 at least once, probably more than 70% of the country, White House coronavirus response coordinator Ashish Jha said Thursday, citing data from the Centers for Disease Control and Prevention (CDC).
Many have been infected multiple times.
In a previous study looking at 257,000 US veterans who had contracted COVID-19 at least once, 12% had a reinfection in April and about 1% had been infected three or more times.
This raises an obvious question:
What is keeping this shrinking minority from getting sick?
Disease experts focus on some predictors beyond individual behavior, such as
genetics, T-cell immunity, and the effects of inflammatory diseases, such
as allergies and asthma.
[The White House says that Biden is improving after contracting COVID-19. She suffers from congestion and fatigue, and had a fever, according to his doctor]
But even as experts learn more about why people may be better able to avoid the coronavirus, they warn that some of these defenses may not stand up to the latest version of the omicron variant, the BA.5, which is remarkably good. in the spread and evasion of vaccine protection.
"It really does take two to tango
," said Neville Sanjana, a bioengineer at the Genome Center in New York.
"If you think about having an infection and anything bad that happens afterward, it's really the product of two different organisms: the virus and the human," he added.
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Genetics May Lower Risk
In 2020, NYU researchers identified a multitude of genes that could influence a person's susceptibility to the coronavirus.
Specifically, they found that inhibiting certain genes that code for a receptor known as ACE-2, which allows the virus to enter cells, could reduce a person's chance of infection.
[What is Paxlovid, Biden's medicine after being infected?]
Sanjana, who led that research, estimated that 100 to 500 genes could influence susceptibility to COVID-19 in places like the lungs or nasal cavity.
Genetics are "probably a big contributor" to protection against COVID-19, he said, "I would never say it's the only contributing factor."
In July, researchers identified a common genetic factor that could influence the severity of a coronavirus infection.
In a study of more than 3,000 people, two genetic variations decreased 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 hospitalization for COVID-19.
Therefore, increasing the expression of the gene should have the opposite effect, that is, reducing the risk of severe disease, although it would not necessarily prevent infection completely.
“It is very natural to get infected once you are exposed.
There is no magic solution for that.
But after you get infected, how you're going to respond to this infection, that's what's going to be affected by your genetic variants," said Ludmila Prokunina-Olsson, principal investigator of the study and head of the Translational Genomics Laboratory at the National Cancer Institute. .
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Still, Benjamin tenOever, a microbiology professor at New York University Grossman School of Medicine who helped conduct the 2020 research, said it will be difficult for scientists to pinpoint a particular gene responsible for preventing a COVID-19 infection. 19.
[COVID-19 Infections Rise Where More Than Half the US Population Lives]
"While there certainly may be some genetics that make people completely resistant, it's going to be incredibly hard to find," tenOever said, "people have been searching hard for two years now with no real results."
T cells could remember previous encounters with coronavirus
Apart from the SARS-CoV-2 coronavirus, there are four other coronaviruses that commonly infect people and often cause mild to moderate upper respiratory illnesses, such as the common cold.
A recent study suggests that repeated exposure to 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 fight off invaders, appear to recognize SARS-CoV-2 based on previous exposure to other coronaviruses.
Thus, when a person who has been infected with a common cold coronavirus is later exposed to SARS-CoV-2, he may not get as sick.
A woman undergoes a COVID-19 test at a pop-up testing center in New York City, on July 11, 2022. BRENDAN MCDERMID/REUTERS
But that T-cell memory likely won't be able to prevent COVID-19 entirely.
"While neutralizing antibodies are key to preventing an infection,
T cells are key to terminating an infection and modulating its severity,
" said Alessandro Sette, study author and professor at the La Jolla Institute of Immunology.
Sette 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 that's what's happening.
“It is possible that, despite being negative in the test, it is a very abortive and transient infection that has not been detected,” Sette said.
At a minimum, he said, T cells from previous COVID-19 infections or vaccines should still offer some protection against coronavirus variants, including BA.5.
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Allergies can provide additional protection
Although asthma was considered a potential risk factor for severe COVID-19 early in the pandemic, more recent research suggests that low-grade inflammation from conditions such as allergies or asthma may have a protective benefit.
“You hear stories about some individuals who get sick and have full symptoms of COVID-19, and who have slept next to their partner for a whole week without infecting her.
People think they must have some genetic resistance to it, [but] a big part of that could be that the partner next to them somehow has a higher-than-normal inflammatory response in their lungs," tenOever said.
According to a study in May,
having a food allergy cut the risk of coronavirus infection in half
in nearly 1,400 American households.
Asthma did not reduce the 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 airway cells, making it harder for the virus to enter.
“Because there are fewer receptors, you will either have a much lower grade infection
or just be less likely to even get infected,” said Tina Hartert, a professor of medicine and pediatrics at Vanderbilt University School of Medicine who co-led that research.
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The study was carried out between May 2020 and February 2021, before the omicron variant emerged.
But Hartert said BA.5 probably wouldn't remove the cross-protection from allergies.
"If something like allergic inflammation is protective, I think that would be true for all variants," Hartert said, "the degree of protection could certainly be different."
Avoiding infection is more difficult with the BA.5 variant
For many, the first explanation that comes to mind when thinking about how to avoid COVID-19 is the level of personal precaution.
tenOever believes that
individual behavior, rather than genetics or T cells, is the key factor
.
He and his family in New York are among those who have never had COVID-19, which he attributes to precautions like staying home and wearing masks.
"I don't believe for a second that we have something special in our genetics that makes us resistant," he said.
It is now known that COVID-19 was easier to avoid before the omicron variant, when a small percentage of infected people were responsible for most of the spread of the virus.
A 2020 study, for example, revealed that 10-20% of infected people were responsible for 80% of transmission.
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But the omicron variant and its sub-variants have made any social interaction riskier for everyone involved.
“Omicron variants are probably more of a level playing field than previous variants,” tenOever said.
BA.5, in particular, has increased the odds that people who have so far avoided COVID-19 will get sick.
President Joe Biden is a good example: he tested positive for the first time this week.
But still, Jha said Thursday,
"I don't think every American gets infected."
