New study reveals increased risk of allergic diseases after COVID-19 infection

By Dr. Liji Thomas, MDReviewed by Lily Ramsey, LLMApr 3 2024

A recent study published in Nature Communications explored the association of COVID-19 with long-term allergic conditions.

Study: Incident allergic diseases in post-COVID-19 condition: multinational cohort studies from South Korea, Japan and the UK. Image Credit: wavebreakmedia/Shutterstock.com

Background

The severe respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in late 2019, and led to the declaration of a coronavirus disease 2019 (COVID-19) pandemic in March 2020. It caused over seven million deaths and many times that number of infections and hospitalizations.

Additionally, nearly half of COVID-19 cases have to deal with delayed or chronic morbidity, which may have set in during or after the acute phase of infection. These are called post-COVID-19 conditions or post-acute sequelae of COVID-19 (PASC), otherwise known as long COVID.

Symptoms of PASC, in some cases, include immunologic phenomena that may cause allergic conditions of various kinds.

About the study

The study aimed to investigate how ethnicity affects allergic conditions following COVID-19. Researchers formed a synthetic group comprising over 22 million individuals from South Korea, Japan, and the UK, drawing participants from multinational studies to represent these ethnic backgrounds. S

pecifically, the South Korean segment included more than 800,000 people with an average age of 48. From the UK and Japan, the cohorts included over 325,000 and 2.5 million participants, respectively.

Within these groups, approximately 150,000 participants from South Korea, 77,000 from the UK, and 542,000 from Japan had been infected with SARS-CoV-2. This large-scale analysis aimed to shed light on the ethnic variations in post-COVID-19 allergic reactions.

What were the findings?

After adjusting for all known variables that could affect the outcome, the researchers discovered that individuals infected with SARS-CoV-2 showed a 20% higher occurrence of allergic diseases compared to those not infected.

This increased risk was consistent for infections from both the original and Delta variants of the virus. Specifically, the likelihood of developing asthma in those infected was more than double, at 2.25 times that in non-infected individuals.

The chance of getting allergic rhinitis was 25% higher in the infected group, though no significant increase was observed for food allergies or atopic dermatitis.

Moreover, while the risk for allergic diseases decreased over time after the infection, it didn't disappear entirely. This decrease in risk varied from country to country.

Severity of infection and allergy risk

Moderate-to-severe COVID-19 was linked to a 50% higher risk of overall allergy, compared to 14% among those with mild disease.

COVID-19 vaccination and allergy risk

Those who had received the vaccine had a 44% higher risk of allergy (with one dose). This was reduced by 20% after two doses of the vaccine. The two-dose cohort had comparable allergy risk as the controls, both overall and for the various allergy subgroups.

Other factors like coexisting morbidity, drinking, body mass index, exercise, and the SARS-CoV-2 strain responsible for the infection, did not show significant correlation with allergy risk.

Conclusions

“This is the first study that provides comprehensive evidence for the association between SARS-CoV-2 infection and subsequent incident allergic outcomes.”

It emphasizes the relationship between COVID-19, especially moderate to severe, and subsequent allergy onset. It also indicates that COVID-19 vaccination with at least two doses weakens the risk of new allergies.

The findings broadly corroborate earlier research, but there is a need for more studies on the allergic sequelae of COVID-19 on a larger and more multinational scale.

Multiple pathways have been proposed to account for the observed correlations, including T cell disruption, regulatory T cell (Treg) disturbances, and the cytokine storm in acute severe COVID-19.     

Over time, the virus may be slowly cleared from the host, especially if adaptive immunity has been strengthened by vaccination against the virus.

The study underlines “a need for persistent health policies to manage the severity of SARS-CoV-2 infection.” People with a history of COVID-19 should be aware that they are at higher risk for allergic manifestations in the short-term future, at least.