## 1 Introduction  
Asthma is a common chronic respiratory disease usually characterized by chronic airway inflammation and a combination of variable respiratory symptoms and expiratory airflow limitation [1]. Asthma affects people of all ages and is associated with significant morbidity and mortality. Its prevalence varies according to different age groups and countries and is influenced by many other variables, including definition and setting. The overall prevalence in 2019 ranged from 5.4 to 9.8%, based on different definitions of asthma [2]. However, there is a significant variation (1-18%) between different countries [1,2]. Adult patients with asthma are frequently admitted to the Emergency Department (ED) for exacerbations or uncontrolled symptoms [3]. Different well-known triggers, including viral respiratory infections, can modify the airway hyper-responsiveness typical of asthma, leading to airway obstruction and rapid worsening of respiratory symptoms [4]. The pandemic associated with SARS-CoV-2 infection has affected hundreds of millions of people worldwide due to its high prevalence and rapid transmission [5]. Symptoms and disease severity are extremely variable. The clinical manifestations of SARS-CoV-2 infection may involve different organs or systems, i.e., gastrointestinal, cardiovascular, nervous, and hematological, among others. However, the most common complication is an interstitial pneumonia that could be associated with different degrees of respiratory failure, up to and including acute respiratory distress syndrome [6]. Millions of deaths occurred worldwide due to severe clinical forms of COVID-19, mainly due to such respiratory complications. Several factors, some virus-related (such as viral load and variant) and some host-related (including age, gender, and comorbidities), play a role in determining the clinical picture of SARS-CoV-2 infection [7]. On the other hand, the availability of specific vaccines has radically changed the course of COVID-19. Full vaccination with booster doses has been associated with a significant improvement in clinical outcome, especially in high-risk patients, such as the elderly and frail [8; 9]. Regarding comorbidities, initially asthma, like other chronic lung diseases, was considered a risk factor for severe COVID-19. Several studies on the relationship between asthma and COVID-19 have since been published. They were extremely heterogeneous in terms of sample size, population, design, and setting, providing conflicting results. Most of them concluded that asthma was not a risk factor for severe COVID-19, sometimes even suggesting a protective role [10; 11; 12; 13; 14]. However, other studies reported that asthma was associated with a worse outcome [15; 16; 17]. Furthermore, most of the available data on the relationship between asthma and COVID-19 comes from large national datasets or retrospective cohorts of patients hospitalized for COVID-19. However, both are associated with possible bias. In fact, the former allow the collection of data on large samples, but is often less precise and accurate, while the latter guarantee higher quality results, but regarding from the most seriously ill patients. Our hypothesis is that the emergency department is the best environment to study the interaction between asthma and SARS-CoV-2 infection as, globally, it is the true watershed between primary healthcare and the hospital. Only two retrospective cohort studies of asthma and COVID-19 patients in the emergency room are currently available [18; 19]. In addition to the prevalence of asthma, these studies assessed only one or two general outcomes, such as hospitalization and/or mortality rate. In a preliminary study by our group on COVID-19 patients consecutively enrolled in an Italian ED during the first pandemic wave, the prevalence of asthma was very low (2.5%), and the risk of hospitalization was significantly lower compared to that of non-asthmatics [14].