Children and adolescents with allergy and/or asthma seem to be protected from coronavirus disease 2019

To the Editors:

Akenroye et al¹ discussed the use of corticosteroids and biologics in asthma during coronavirus disease 2019 (COVID-19) pandemic. COVID-19 began in the People's Republic of China and rapidly spread worldwide.² Italy was the first European country involved in the pandemic and the first cluster occurring in South Lombardy. The novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), penetrates the host cells binding to the angiotensin-converting enzyme 2 (ACE2) receptors.

Initially, asthma was considered a risk factor for severe COVID-19. However, a preliminary study reported that no hospitalized patient had asthma or allergies.³ Consistently, another Chinese study reported an asthma prevalence of 0.9% in inpatients with COVID-19, which is substantially lower than in the general population (6.4%).³ In contrast, eosinopenia has been associated with poor COVID-19 prognosis.⁴ Eosinophil responses to COVID-19 have been recently discussed.⁵ Eosinophils orchestrate the immune response to a respiratory virus, releasing cytotoxic proteins, increasing nitric oxide, producing type 1-associated cytokines, mainly interleukin 12 (IL-12) and interferon gamma, and recruiting CD8 T lymphocytes. Eosinophils clear viral load; thus, guaranteeing recovery from viral infections. Patients with allergy usually present with eosinophilia as a mechanism of protection against infections; however, it is well known that patients with allergy, such as those who have asthma, are more susceptible to viruses. Coronavirus is, however, scarcely associated with asthma exacerbations. Nevertheless, anti–IL-5 biologics, including mepolizumab, deplete eosinophils, and, theoretically, could promote viral infections.

Considering this background, we present our data concerning both COVID-19 in children and adolescents and mepolizumab treatment in patients with severe asthma. We considered the records of the following 2 hub hospitals: (1) South Lombardy, which started the first Italian cluster; and (2) Liguria, a neighboring region. Concerning eosinophil count, patients with allergy had higher values than inpatients with COVID-19 (median values 423 and 112 cells/μL, respectively). A total of 5 patients (mean age 22.4 years, 3 men) were treated with mepolizumab for at least 12 months and had levels of 319 eosinophils/μL (median value). Therefore, α–IL-5 biologic did not completely abolish eosinophilopoiesis. Patients with asthma were well-controlled and significantly reduced the rate of asthma exacerbations in the previous year. Notably, none of them suffered from COVID-19, at least to date.

Moreover, we considered the young people admitted to the 2 hub hospitals for COVID-19. Of the 52 patients hospitalized for COVID-19 (24 boys, mean age 6.2 years), only 1 required high-level care. Interestingly, only 2 patients (4%) were allergic (atopic dermatitis and allergic rhinitis), and only 1 patient (2%) has asthma. The prevalence of allergy and asthma is 32% and 11%, respectively, in this geographic area (Fig 1). These outcomes are consistent with the literature data and pathophysiologic mechanisms. Young people are spared from SARS-CoV-2 infection probably because of the highly expressed thymic repertoire and activated innate and adaptive immunity.⁶ Patients with allergies are rare in the COVID-19 population, and these outcomes suggest that allergy could be a protective factor for coronavirus infections. To further support this hypothesis, a very recent study provided evidence that allergic sensitization was inversely related to ACE2 expression, and natural exposure to an allergen and subsequent challenge significantly reduced ACE2 expression.⁷ In conclusion, it seems that allergy and controlled asthma could be partially protected from COVID-19. Moreover, corticosteroids and biologics could be reasonably continued.