It’s harder for kids with food allergies to catch COVID
Two and a half years after the coronavirus pandemic began, there’s growing evidence that allergies–which were once suspected to put patients at risk for serious COVID-19–instead protect against the illness. Children with allergies are significantly less likely to catch COVID-19, for reasons that may have to do with the idiosyncrasies of the virus, according to a long-term, National Institutes of Health-funded study published earlier this month.
” “Historically, people with asthma and allergic diseases are susceptible for poor outcomes because of viral infections,” said Max Seibold who was a pediatrician at the National Jewish Health in Denver and led the research. “There was real concern about whether this was a risk category .”
Asthma and atopic dermatitis, the most common form of eczema, and food allergies are loosely grouped together as “allergic disorders,” partly because they tend to develop together. Seibold states that it’s not common for everyone with atopic dermatology to have food allergies [or]. But they do occur together. “But it occurs concurrently in enough individuals that we know there’s likely something underlying it mechanistically.” And people with allergic disorders share a specific type of inflammation, called Type 2 inflammation.
The immune system uses Type 1 inflammation to fight viral infections. For people with allergic disorders, a viral illness can set off both inflammatory alarms. Seibold states that people with allergic disorders can have a “flamed-out” state in which their airways are clogged up with both types of inflammation. This can lead to more severe illnesses.
Beginning in the spring of 2020, the team of researchers from multiple US institutes recruited children and teenagers from 12 different US cities who were already participating in allergy or asthma studies, as well as their primary caregivers. Every two weeks between May 2020 and February 2021, 5,600 participants were tested for COVID, with additional testing for anyone who became ill.
This allowed the study authors to track not only serious or symptomatic COVID cases (which are rare in children), but also asymptomatic cases. They calculated the risk of infection and risks of serious illness from this data. Because it is difficult to collect data on asymptomatic infections, it is rare for COVID studies to estimate the overall infection rate. Seibold states that it was a difficult task to enroll a group and collect samples over a long time.
Over the course of the study, a quarter of all households, and around 14 percent of all participants, caught COVID.
This infection rate suggests that COVID has spread further than previously thought. “We found that 75 percent of infections in kids were asymptomatic,” Seibold says. “When we compare our data with CDC data over the same period, we find a much higher likelihood of infection for children.” These kids also had high viral loads, even though they were not symptomatic, which suggests that they could spread the disease.
Allergy diseases had a negative impact on COVID risk, but not in the way researchers would expect. People with food allergies were 50 percent less likely to catch COVID, and household transmission was much lower when someone had an allergy. Atopic dermatitis didn’t affect risk. Atopic dermatitis did not affect risk, unless asthma was caused by allergic reactions.
When Seibold was asked why, he said, “The first thing that I would say is, ‘We don’t know.’ “
But the team has a guess. Type 2 inflammation is caused by proteins that alter the function of cells, especially in the skin and respiratory tract. Seibold states that Type 2 inflammation can alter the expression of thousands of genes. It’s a powerful mechanism. You can affect many things at once, but you might also modify one aspect of the biology that has an effect on another, such as SARS-CoV-2 risk
An earlier study by Seibold, co-authors showed that people with high levels of Type II inflammation had lower levels of ACE2 in their cells. ACE2 is the receptor that SARS/CoV-2 latches onto when it infects cells. This suggests that people with allergies are less vulnerable to the virus at the cellular level.
“It is not a foolproof tale,” Seibold states. “Why is asthmatic, for example, not ?”
The answer to that question could lie in another study from 2019, which found that kids with food allergies had much stronger Type 2 inflammation signatures than those with allergic disorders of the skin. “I think the food allergic individuals have the most extreme levels of Type 2 inflammation and therefore the biggest effect on their receptor,” Seibold says, before cautioning: “that’s all conjecture.”
He summarizes the hypothesis as follows: Allergy sufferers with allergies have their ACE2 receptors reduced by inflammation. This should reduce infection risk. It’s not proved. Seibold states that “We have A-B and B-C, but that’s a little bit different than going from one A to the other,”
The team is currently studying the cells of participants using RNA sequencing. This could reveal whether participants who were previously identified as having low COVID risk had actually experienced the high inflammation and decreased ACE2 predicted by other studies.
These findings are consistent with other studies on allergies, SARS-CoV-2, and SARS. A study published in March found that when lung cells were exposed to another key marker of type 2 inflammation, they cleared SARS-CoV-2 virus faster. And people with allergic diseases were about 25 percent less likely to be infected, according to an observational study in the UK published in late 2021.
Cezmi Akdis, editor of the journal Allergy and the director of the Swiss Institute of Allergy and Asthma Research, wrote in an email: “Although the publications are controversial, I think that existing allergy prevents severe COVID development.”
Seibold isn’t interested in drawing wider conclusions about the relationship between allergy and infections. He says, “I’m not certain that there’s any strong conceptual connection” between this virus and the course allergic diseases. “It’s possible that there are two independent things that occur–it’s just the way things play out sometimes .”
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