Four years after the beginning of the <scp>COVID</scp>‐19 pandemic and the publication of the first case series
Authors: Ya‐dong Gao, Cezmi A. Akdis
Journal: Allergy (2024)

On February 19, 2020, Allergy published its first COVID-19 article online.1 Noticeably, this study was published ahead of the first case of COVID-19 in Europe which was reported on February 21, 2020 in Italy. This case series by Zhang et al. demonstrated that human-to-human contact is essential for the spread of the disease and described the detailed clinical, laboratory, and radiology characteristics of 140 hospitalized COVID-19 patients in Wuhan, China. This study suggested for the first time that asthma and allergy are not susceptible factors for SARS-CoV-2 infection.1 Subsequent studies supported this finding and showed that type 2 inflammation is associated with a lower risk of infection and better outcomes of COVID-19.2 Eosinopenia, together with lymphopenia, was proposed as an important biomarker for severe COVID-19 and worse outcomes.3 From then on, 359 publications relevant to many aspects of allergy, immunology, and COVID-19 have been published in Allergy. These studies timely conveyed useful information of clinical features as well as the immunological mechanisms of COVID-19 to readers and provided guidance on correct diagnosis and treatment of allergic diseases during the pandemic, on how to dealing with allergic reactions of COVID-19 vaccines and on vaccination strategies in individuals with previous allergy to vaccines. Through the joint efforts of editors and authors, Allergy contributed greatly to the global prevention and treatment of COVID-19. Looking back at these articles, we can divide them into the following categories: clinical manifestations and risk factors for infection, progression to severe disease, and worse outcomes2, 4-8; underlying immunological mechanisms of COVID-199-11; guidelines and position papers about the regulation of clinical practice during the COVID-19 pandemic, including the use of biologicals and inhaled or intranasal corticosteroids, handling allergen immunotherapy.12, 13 In addition, studies associated with COVID-19 vaccines, including allergic reactions to vaccines and guidelines on dealing with anaphylaxis caused by COVID-19 vaccines, antibody responses to different vaccines14, 15; and the short- and long-term impacts of COVID-19 on allergic disease, including the incidence and severity, treatment response of common allergic diseases2, 16 have been published. On April 02, 2020, Dong et al. described the clinical manifestations of 11 COVID-19 model cases to provide a clearer picture of the wide range of clinical features of COVID-19.4 These cases included patients of asymptomatic infection, mild symptoms, negative virus nucleic acid test but positive antibody test, positive virus nucleic acid test after recovery, secondary pneumonia, pneumonia in patients with allergy, chronic obstructive pulmonary disease (COPD), etc.4 Cai et al. found that during the first wave of the pandemic, COVID-19 patients outside Hubei presented mostly with mild disease and better outcomes, suggesting that sufficient medical resources will improve the treatment and outcomes of COVID-19.6 Du et al. investigated 182 hospitalized children with COVID-19 and found that most children were asymptomatic and nonsevere, and having an allergic disease did not affect the susceptibility, clinical features, laboratory, and immunological responses of pediatric COVID-19.7 Zhang et al. analyzed 289 hospitalized COVID-19 patients and found that elder age, more infected lobes, elevated C reactive proteins (CRP) levels on admission, chest tightness, smoking history, persistent inflammation, and sustained decrease in counts of lymphocytes, eosinophils, and platelets were independent risk factors for the death of severe patients.5 In addition, the patient's individual demographic characteristics, socioeconomic status, lifestyle, as well as underlying comorbidity including chronic diseases, tumors, diabetes, immunodeficiency, and pregnancy are risk factors for the progression of COVID-198 (Figure 1). Several EAACI statements and position papers were published during this period to guide the management of allergic diseases, the conductance of allergen immunotherapy (AIT) during the pandemic of COVID-19.12, 13 The underlying mechanisms of allergy and type 2 inflammation on COVID-19 susceptibility were another research hotspot during the first wave of COVID-19. To investigate the expression patterns of potential receptors for SARS-CoV-2, including ACE2, TMPRSS2, CD147, cyclophilins, and CD26, Radzikowska et al. reported on RNA sequencing in airway epithelial cells and lung tissues from healthy subjects and individuals with risk factors and comorbidity for COVID-19.11 Following this, it was shown that the type 2 inflammation-associated cytokine IL-13 decreased the expression of ACE2 in bronchial epithelial cells.17 Early reviews highlighted for the comprehensive understanding of the cellular and antibody responses to SARS-CoV-2 and the underlying mechanisms of immunopathology of COVID-19,9 and now direct tissue damage by SARS-CoV-2, lymphopenia and eosinopenia, cytokine storm, B cell dysfunction and insufficient antibody responses to SARS-CoV-2, deficiency in interferon production, autoantibodies, et al., have been proposed for better understanding the immune responses of COVID-19 (Figure 2). The impact of AIT, biologicals, and topical and oral corticosteroids on the disease course, severity, and outcomes of COVID-19 has gained the attention of many readers.18 Vaccination for COVID-19 has become the central topic after the availability of COVID-19 vaccines, including the strategies for the development of COVID-19 vaccines, the varied protective effects of different types of COVID-19 vaccines, potential impacting factors of individual's antibody responses, allergic reactions to these vaccines, and components responsible for the anaphylaxis. An EAACI position paper was released to guide the management of anaphylaxis and the vaccination strategy in the context of preexisting allergy or previous anaphylaxis to COVID-19 vaccines.15 The short- and long-term impact of COVID-19 on allergic diseases has been a subject of concern for experts in the allergy field. It was reported that COVID-19 may increase the risk of developing atopic dermatitis16 and the prevalence of pruritus and leukocytoclastic vasculitis.19 Type 2 asthma was associated with less chest pain and the necessity of long-acting muscarinic agonist use 12 months after COVID-19.20 Long COVID-19 is associated with diverse symptoms and persistent inflammation, mast cell activation, autoantibodies, and lymphopenia.2 In summary, these timely published papers in Allergy in the early days of the COVID-19 pandemic originally addressed almost all relevant questions in the context of allergy and asthma and will have a lasting impact on the prevention and treatment of COVID-19, considering the potential of long-term coexistence of SARS-CoV-2 with humans. None. None of the authors have a conflict of interest to disclose. Data sharing is not applicable to this article as no new data were created or analyzed in this study.