Most people in the US have had COVID-19 at least once – more than 70% of the country’s, White House COVID-19 response coordinator Ashish Jha Told on Thursday, citing data from the Centers for Disease Control and Prevention.
Many people have been infected many times. one in preprint In a study looking at 257,000 US veterans who had gotten COVID at least once, 12% had re-infection by April and about 1% had been infected three times or more.
This raises an obvious question: what is stopping that shrinking minority of people from getting sick?
Pathologists are looking beyond individual behavior to some predictive factors, including genetics, T cell immunity, and the effects of inflammatory conditions such as allergies and asthma.
But as experts learn more about the reasons why people may be able to avoid COVID, they caution that some of these defenses may not hold up against the latest version of Omicron, BA.5, which Vaccines are remarkably good at spreading and developing protection. ,
“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 happens after that, it’s really a product of two different organisms: viruses and humans.”
Genetics may reduce risk of covid
In 2020, NYU researchers identified a multitude of genes Which can affect a person’s susceptibility to the coronavirus. Specifically, they found that blocking certain genes that code for a receptor called ACE-2, which allows the virus to enter cells, could reduce a person’s chances of infection.
Sanjana, who carried out that research, estimated that around 100 to 500 genes may affect susceptibility to COVID-19 in sites such as the lungs or nasal cavity.
Genetics is “likely to be a major 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 affect the severity of coronavirus infection. one in study In more than 3,000 people, two genetic variations 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.
Again, increasing gene expression should have the opposite effect – reducing the risk of serious disease – although it may not necessarily prevent infection completely.
“It’s very natural to get infected once you’ve been exposed to it. There’s no magic bullet for it. But once you’ve been infected, how you’re going to react to this infection, that’s going to be affected by your genetic variants, ” What was said. Lyudmila Prokunina-Olson, lead researcher of the study and head of the Laboratory of Translational Genomics at the National Cancer Institute.
Still, Benjamin Tenover, a microbiology professor at NYU Grossman School of Medicine who helped conduct the 2020 research, said it would be difficult for scientists to pinpoint a particular gene responsible for preventing COVID infection.
“While there certainly still may be some genetics that make people completely resistant, they’re going to be incredibly hard to find,” Tenover said. “People are already watching intensely for two years now with no real results.”
T cells can remember past coronavirus encounters
In addition to this new coronavirus, SARS-CoV-2, four other coronaviruses commonly infect people, most commonly causing mild to moderate upper respiratory illnesses such as the common cold.
a recent study suggested that repeated exposure to these common colds or occasional infections may provide some protection against SARS-CoV-2.
The researchers found that T cells, a type of white blood cell that recognize and fight invaders, recognize SARS-CoV-2 based on previous exposure to other coronaviruses. So when someone who has been infected with the common cold is later exposed to SARS-CoV-2, they may not be as sick.
But that T cell memory might not stop COVID completely.
“While neutralizing antibodies is important for preventing infection, T cells are important for eliminating infection and controlling the severity of infection,” said study author Alessandro Sete, a professor at the La Jolla Institute for Immunology.
Sete said it is possible that some people’s T cells clear the virus so quickly that the person never tests positive for Covid. But researchers aren’t yet sure what’s going on.
“It’s possible that, despite being negative on the test, it was a very abortive, transient infection that went undetected,” Sete said.
At the very least, 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 thought to be a potential risk factor for severe COVID earlier in the pandemic, 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 people getting sick and having full-blown symptoms of COVID, and sleeping with their partner for a whole week during that period. People think they must have some genetic resistance to it. For, [but] A big part of this may be if their partner has a higher than normal inflammatory response to their lungs in any way,” Tenover said.
a May study found that having food allergies in nearly 1,400 American homes cut the risk of coronavirus infection in half. Asthma didn’t reduce people’s risk of infection in the study, but it didn’t increase it either.
According to the researchers, one theory is that people with food allergies express fewer ACE2 receptors on the surface of the cells of their airways, making it harder for the virus to enter.
“Because there are fewer receptors, you’ll either have a very low-grade infection or be even less likely to get infected,” said Tina Hartert, a professor of medicine and pediatrics at Vanderbilt University School of Medicine. ,
The study took place from May 2020 to February 2021, before the Omicron version came out. But Hartert said BA.5 likely won’t eliminate cross-protection from allergens.
“If something like allergic inflammation is protective, I think it would be true for all types,” Hartert said. “The extent to which this can be protective can certainly vary.”
BA.5. It is more challenging to avoid infection with
For many, the first explanation that comes to mind when thinking about prevention from COVID is the individual level of caution. Tenover believes that individual behavior, more than genetics or T cells, is the dominant factor. He and his family in New York City are among those who have never had COVID, which he attributes to precautions like staying home and wearing a mask.
“I don’t think for a moment that there is anything special in our genetics that makes us resistant,” he said.
It is now common knowledge that it was easier to avoid COVID before Omicron, when a small percentage of those infected were responsible for the spread of the virus. a 2020 studyFor example, it was found that 80% transmission occurs in 10-20% of infected people.
But Omicron and its subtypes make any social interaction risky for everyone involved.
“It’s probably a level playing field with the Omicron variant compared to the earlier variants,” Tenover said.
BA.5 has increased the chances of getting sick especially for those who have survived Covid so far. President Joe Biden is a prime example: He tested positive for the first time this week.
But still, Jha said on thursday“I don’t believe every American will be infected.”