Compared to patients with asthma of Th2-low endotype, those with Th2-high endotype show higher responsiveness to corticosteroid treatment
[27]. As corticosteroids have immunosuppressive effects, the impact of corticosteroids on COVID-19 outcomes may be concerning for many clinicians
[28]. Previous studies of corticosteroid treatment during respiratory viral illness, including SARS, have generally shown a lack of effectiveness in reducing morbidity and instead, possible harm
[29][30]. Earlier in the pandemic, when COVID-19-specific evidence relating to corticosteroid use was still largely lacking, the World Health Organization (WHO) initially recommended against the use of systemic corticosteroids to treat COVID-19 in its clinical management guidance document released in March 2020
[31]. However, as studies evaluating various treatments, including corticosteroids, in patients with COVID-19 have rapidly accumulated, the WHO changed its stance in a guidance document released in September 2020, which stated a strong recommendation for the use of systemic corticosteroids in the treatment of patients with severe and critical COVID-19 based on the most current evidence
[32]. The updated WHO guidance specifically referenced the preliminary report of the now published RECOVERY multicenter, randomized controlled trial, which included 6425 hospitalized patients with COVID-19 who were randomized to receive oral or intravenous dexamethasone 6 mg once daily in addition to usual care or usual care alone
[33]. Final results of the RECOVERY study showed that dexamethasone-treated COVID-19 patients had a significantly lower risk of the primary outcome of 28-day mortality compared to those who received usual care alone (age-adjusted rate ratio, 0.83; 95% CI, 0.75–0.93;
p < 0.001)
[33]. However, in the subgroup analysis according to respiratory support at randomization, mortality risk was significantly reduced in patients requiring invasive mechanical ventilation or oxygen only, but was not significantly reduced in patients who did not require respiratory support. In the PRINCIPLE study
[34], which is a randomized controlled trial, older non-hospitalized patients with COVID-19 (65 years of older or 50 years or older with comorbidities) who received inhaled budesonide 800 µg twice daily for 14 days in addition to usual care had a significantly shorter time to recovery by approximately 3 days compared to those who received usual care alone.
The burden of COVID-19 among patients with chronic respiratory diseases has not been shown to be increased, and indeed was shown to be decreased in some studies, compared to the general population
[35]. This rather unexpected finding has been hypothesized to be attributed to potential protective effects of respiratory disease treatments against SARS-CoV-2 infection and severe disease. Observational studies have shown that inhaled corticosteroid use in patients with asthma was associated with the increased prevalence of non-COVID-19 upper and lower respiratory tract infections
[36][37]. In contrast, inhaled corticosteroid treatment has been associated with a reduced expression of ACE2, the entryway of SARS-CoV-2 into host cells, thereby potentially reducing SARS-CoV-2 susceptibility and morbidity
[38][39]. Results of an in vitro study have shown that pre-treatment of human nasal and tracheal epithelial cells with budesonide, glycopyrronium, and formoterol inhibited coronavirus HCoV-229E replication and cytokine production
[40]. An in vitro study has revealed that the corticosteroids mometasone and ciclesonide suppressed replication of SARS-CoV-2 in a culture medium of infected cells, and that ciclesonide was particularly effective in a concentration-dependent manner
[41]. Furthermore, a study that screened a panel of 48 United States Food and Drug Administration-approved drugs identified ciclesonide as an inhibitor of SARS-CoV-2 cytopathic viral activity
[42]. In addition to the inhibitory effects on viral replication, treatment with corticosteroids might also reduce the severity of COVID-19 by inhibiting virus-induced cytokine release and dampening the exaggerated inflammatory response responsible for severe symptoms
[43]. Overall, the effects of the appropriate use of oral and inhaled corticosteroids is expected to lean toward being beneficial rather than harmful for patients with asthma during the pandemic, and adherence to all maintenance asthma medications to ensure good symptom control and to prevent exacerbation should be emphasized, as is consistently recommended by professional organizations worldwide
[44].