In an analysis of 13 published prospective studies of people of all ages with confirmed SARS-CoV-2 infection who were followed up for at least 12 months, pre-existing allergic conditions were linked to higher risks of experiencing long COVID, according to a study today in Clinical & Experimental Allergy.
This is one of the first studies to assess the relationship between long COVID and allergies.
The studies included 9,967 participants and were published from January 1, 2020, to January 19, 2023. For long COVID, the authors used a definition of self-reported or physician-diagnosed symptoms continuing or developing after acute COVID-19 onset.
In the 13 included studies, the proportion of people with long COVID ranged from 11% to 90%, with a median of 53.3%. Study sample sizes ranged from 39 to 2,826 people.
Associations with asthma, allergic rhinitis
Four of the 13 studies provided estimates on the association between pre-existing allergic conditions such as asthma or hay fever and long COVID. Pre-existing asthma was associated with an increased risk of long COVID, but the evidence was very uncertain, the authors said. The odds ratio (OR) for preexisting asthma and long COVID was 1.94 (95% confidence interval [CI], 1.08 to 3.50).
In an analysis of three studies that included data on preexisting allergic rhinitis, the condition was significantly associated with an increased risk of long COVID (OR, 1.96; 95% CI, 1.61 to 2.39).
We need a better, harmonized definition of what is considered Long-COVID for epidemiological studies of this sort.
Only 3 of the 13 studies measured long COVID with physical examinations and comprehensive questionnaires, the authors cautioned. Moreover, among the 13 studies, the authors found a high risk of bias due to patient selection (mostly hospitalized patients) and loss to follow-up.
"We need a better, harmonized definition of what is considered Long-COVID for epidemiological studies of this sort. Regardless we will be updating our analysis once further studies have been published in the next few months," said senior author Christian Apfelbacher, PhD, of the Institute of Social Medicine and Health Systems Research, in Germany, in a press release on the study from the journal's publisher.