Food allergies can reduce the risk of COVID

Two-and-a-half years after the start of the Coronavirus pandemic, there is growing evidence that allergies (which once suspected patients were at risk of severe COVID-19) protect against the disease. Children with allergies are less likely to catch COVID-19 for reasons that may be related to the idiosyncrasy of the virus, according to a long-term study funded by the National Institutes of Health published earlier this month.

“Historically, people with asthma and allergic disease have poor results from viral infections,” says Max Seibold, a pediatrician and genomics researcher at Denver National Jewish Health Hospital who led the study. “There was a real fear that there was a risk group there.”

Asthma, atopic dermatitis, the most common eczema, and food allergies are associated with “allergic diseases” in part because they tend to develop together. “Not everyone with atopic dermatitis has a food allergy [or] he has asthma, ”says Seibold. “But at the same time it happens enough in individuals. We know there’s something mechanically beneath that.” And people with allergic disorders share a specific type of inflammation, called type 2 inflammation.

The immune system uses another type of inflammation, mainly type 1, to fight viral infections. But for people with allergic disorders, a viral infection can trigger two inflammatory alarm bells. “They have this kind of condition in their airways where two types of inflammation occur at the same time,” says Seibold, which can lead to more serious illnesses.

Beginning in the spring of 2020, a team of researchers from several U.S. institutes hired children and teens from 12 U.S. cities and their primary caregivers who were participating in allergy or asthma tests. Every two weeks between May 2020 and February 2021, 5,600 participants were tested for COVID-19, with additional tests for anyone who became ill.

In this way, the researchers followed not only symptomatic or severe cases of COVID (which are still rare in children), but also asymptomatic ones. Based on these data, they calculated the risk of general infection and the risk of serious illness. Calculating the overall infection rate is a rarity among COVID research because it is very expensive to collect data on asymptomatic infections. “It was a big commitment to enroll a team and receive their samples regularly for a long time,” says Seibold.

During the study, a quarter of all households and about 14 percent of all participants caught COVID.

[Related: CDC estimates 58 percent of Americans have been infected with COVID so far]

This rate of infection suggests that COVID has spread more widely than previously thought. “We saw that 75 percent of children’s infections were asymptomatic,” says Seibold. “If you align our data with the CDC at the same time, we will have a much higher probability of infecting children.” And these children had a high viral load, even if they were asymptomatic, suggesting that they could spread the disease.

Allergic diseases were at risk for COVID, but not as the researchers had hoped. People with food allergies had a 50 percent lower chance of catching COVID, and home transmission was much lower when someone was allergic to it. Atopic dermatitis did not pose a risk. Not even asthma, unless it is asthma caused by allergic reactions.

Asked why this would be the case, Seibold says: “The first thing I would say is, ‘We don’t know.’ ”

But the team has an invention. Proteins that cause inflammation of type 2 can alter the functioning of cells, especially in the skin, respiratory tract, and other membranes. Type 2 inflammation can alter the expression of thousands of genes, says Seibold. “It’s a very powerful mechanism. If you are affected by many things, you may be able to shape some aspects of the biology that affect something else, such as the risk of SARS-CoV-2.

In particular, previous work by Seibold and co-authors showed that people with high levels of type 2 inflammation had less protein called ACE2 in their respiratory cells. ACE2 is a specific receptor that binds when it infects SARS-CoV-2 cells. This suggests that people with allergic disorders are less vulnerable to the virus at the cellular level.

“It’s not a story at all,” Seibold says. “Why aren’t asthmatics, for example, protected?”

The answer to that question may lie in another 2019 study, which found that children with food allergies had much stronger inflammatory signatures of type 2 than those with allergic skin disorders. “I believe that allergic foods have the most extreme levels of type 2 inflammation and therefore have the greatest impact on their receptors,” says Seibold, before warning, “that’s all speculation.”

He summarized the hypothesis as follows: Inflammation reduces ACE2 receptors in people with allergies. This in turn should reduce the risk of infection. But it has not been proven. “We have it from A to B and B, but that’s a little different than going from A to B to C,” Seibold says.

Right now, the team is studying the cells of the participants through RNA sequencing. This may indicate whether participants with low COVID risk had high inflammation and reduced ACE2 predicted in other studies.

The findings are consistent with other studies on allergies and SARS-CoV-2. A study published in March found that when lung cells were exposed to another major marker of type 2 inflammation, the SARS-CoV-2 virus cleared faster. And people with allergic diseases were about 25 per cent less likely to be infected, according to an observational study in the UK published in late 2021.

Cezmi Akdis, editor of the magazine Allergy and the director of the Swiss Institute for Allergy and Asthma Research wrote in an email: “Although the publications are controversial, I believe that the existing allergy prevents serious development of COVID.”

However, Seibold does not want to draw any broader conclusions about the relationship between infections and allergies. “I’m not sure there is a strong conceptual relationship” between this virus and the evolution of allergic diseases, he says. “Two independent things can happen, sometimes how things work out.”

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