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Allergies linked to heightened risk of long COVID, recent review suggests

In a recent study published within the journal Clinical & Experimental Allergy, a team of scientists conducted a scientific review to know whether allergic diseases resembling asthma and allergic rhinitis were risk aspects for long coronavirus disease (long COVID).

Study: Allergic diseases as risk aspects for Long-COVID symptoms: Systematic review of prospective cohort studies. Image Credit: p.unwell.i / Shutterstock


Long COVID, also generally known as post-COVID syndrome or post-acute sequelae of COVID-19 (PASC), has rapidly change into a big health concern within the wake of the coronavirus disease 2019 (COVID-19) pandemic. It constitutes the persistence or reoccurrence of COVID-19 symptoms beyond 12 weeks after contracting the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, where the symptoms can’t be explained by an alternate diagnosis. Long COVID often impacts multiple organ systems, with dyspnea and fatigue being essentially the most common symptoms. In severe cases, symptoms related to the cardiovascular, nervous, and gastrointestinal systems have also been observed.

Long COVID symptoms have been observed to persist for greater than a 12 months, and there have been no established links between the severity of the SARS-CoV-2 infection and the event of long COVID. The shortage of clarity concerning the epidemiological basis of long COVID has impacted the event of effective treatment and rehabilitation strategies. Moreover, while studies have identified comorbidities resembling obesity, diabetes, and pre-existing pulmonary problems as potential risk aspects for long COVID, there’s a dearth of evidence on the role of allergic diseases resembling allergic rhinitis and asthma in increasing the danger of long COVID.

In regards to the study

In the current study, the scientists conducted a scientific review and comprehensive meta-analysis to look at the association between pre-existing allergic diseases and the increased risk of long COVID and determine the etiology of the disease. Studies published in German or English involving prospective cohorts of all ages that provided information on real-time polymerase chain response (RT-PCR)-confirmed SARS-CoV-2 infections and pre-existing allergic conditions were evaluated. Only studies that had a follow-up period of a minimum of 1 12 months were included.

Long COVID was defined based on physician-diagnosed or self-reported symptoms that continued or developed after an acute SARS-CoV-2 infection. Information on the study setting, study population, COVID-19 diagnoses, exposures consisting of allergies, assessments of exposures, outcomes consisting of long COVID symptoms and duration, and the methodologies for assessing long COVID symptoms were extracted from the studies for evaluation.

Risk of bias was assessed for domains resembling the recruitment and follow-up procedures, definitions and measurement of exposures, the validation of outcomes, evaluation methods, and confounding. Moreover, for every examined consequence, the understanding of evidence was graded for risk of bias, indirectness, consistency, imprecision, and just a few other domains. The meta-analysis was conducted for 4 subsets of study participants based on the presence of asthma in hospitalized individuals, asthma in the overall population, allergies, and allergic rhinitis.


The outcomes suggested that pre-existing asthma in hospitalized individuals and pre-existing rhinitis could increase the danger of long COVID. Nonetheless, the association between pre-existing asthma in the overall population or pre-existing allergies and an increased risk of long COVID was not apparent. The scientists consider that aspects resembling imprecision, indirectness, plausible confounding, and high risk of bias are major contributors to the low certainty of evidence.

The study also discussed among the mechanistic considerations for examining the association between allergic diseases and an increased risk of long COVID. While studies have shown that allergic immune responses involving T-helper lymphocyte type 2 (Th-2) is assumed to supply a certain degree of protection against SARS-CoV-2 infections, it could also increase the danger of long COVID. Understanding the contradicting roles of elevated eosinophil counts and Th-2 activity in COVID-19 and long COVID could help improve therapeutic strategies.

The activation of innate immune responses and the discharge of inflammatory cytokines in response to SARS-CoV-2 infection can also be believed to exacerbate pre-existing allergic diseases or conditions. The review suggested that immunological dysregulation processes resembling elevated interleukin-6 activity should be examined as potential predictors of long COVID.


Overall, the findings indicated that there was a paucity of high-quality research on the involvement of pre-existing allergic diseases in exacerbating the danger of long COVID. This gap might be addressed by improving consequence assessment and exposure validations. The recent consensus on long COVID outcomes defines the Core Consequence Set as consisting of pain, fatigue, post-exertional malaise, changes in work or study, functioning and survival, cardiovascular, nervous, and respiratory system conditions, and mental health and cognitive outcomes.

The authors hope that the defined core outcomes and a clearer assessment of exposures involving distinctions between different allergic diseases will help improve our understanding of the aspects that increase the danger of long COVID. Nonetheless, based on current evidence, they consider that allergic diseases resembling rhinitis and asthma could increase the danger of long COVID.

Journal reference:

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