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Interferon (IFN) has been highlighted in several randomized controlled trials as an attractive therapeutic candidate based plausible mode of action, suppressed response in severe COVID-19, and inhibition of SARS-CoV-2 replication. This study investigated the efficacy and safety of IFN in patients with COVID-19 according to clinical severity. Randomized controlled trials evaluating the efficacy and safety of IFN (systemic or inhaled IFN-α, -β, and -λ) treatment in adult patients with COVID-19 were identified by systematically searching electronic databases until January 2023. Risk of bias were assessed using the Cochrane risk of bias tool, meta-analysis, and certainty of evidence grading were followed for the systematic review. We included 11 trials comprising 6,124 patients. Compared with exclusive standard care or placebo, IFN therapy did not provide significant clinical benefits for mortality at day 28 (pooled risk ratio [RR] = 0.86, 95% confidence interval [CI]: 0.62-1.18, 9 studies, low-certainty evidence) and progression to mechanical ventilation (pooled RR = 1.08, 95% CI: 0.81-1.43, 6 studies, low-certainty evidence) in patients with COVID-19. IFN therapy resulted in significantly increased hospital discharge on day 14 relative to the control arm (pooled RR = 1.29, 95% CI: 1.04-1.59). These results were inconsistent compared to other comparable outcomes such as recovery at day 14 and time to clinical improvement. The IFN-treated arm was as safe as the control arm, regardless of clinical severity (pooled RR = 0.87, 95% CI: 0.64-1.19, 9 studies, low-certainty evidence). In conclusion, IFN therapy was safe but did not demonstrate favorable outcomes for major clinical indices in patients with COVID-19, particularly those with higher than moderate severity. IFN therapy was not associated with worsening outcomes in patients with severe COVID-19. Future clinical trials should evaluate the clinical efficacy of IFN therapy in patients with mild COVID-19 or at an earlier stage. Trial registration: The protocol for this review was prospectively registered in the International Prospective Register of Systematic Reviews (PROSPERO) under the registration number CRD42022301413.

Inhaled corticosteroids are known to be relatively safe for long-term use in inflammatory respiratory diseases and it has been repurposed as one of the potential therapies for outpatients with coronavirus disease 2019 (COVID-19). However, inhaled corticosteroids have not been accepted for COVID-19 as a standard therapy because of its lack of proven benefits. Therefore, this study aimed to evaluate the effectiveness of inhaled corticosteroids in patients with COVID-19. Randomized controlled trials comparing the efficacy of inhaled corticosteroid treatment in patients with COVID-19 were identified through literature electronic database searches up to March 10, 2023. Meta-analyses were conducted for predefined outcomes, and the certainty of evidence was graded using the grading of recommendations, assessment, development, and evaluation approach. Overall, seven trials (eight articles) were included in this systematic review. Compared with usual care, inhaled corticosteroids was associated with significantly improved clinical recovery at 7 and 14 days in patients with COVID-19. In subgroup analysis, only budesonide showed significant efficacy in clinical recovery, whereas no significant benefit was observed for ciclesonide. Moreover, inhaled corticosteroids use was not significantly associated with all-cause hospitalization, all-cause mortality, admission to intensive care unit, or the use of mechanical ventilation. Our systematic review used evidence with very low to moderate certainty. Although based on limited evidence, our results suggest that inhaled corticosteroids treatment, especially budesonide, improves the clinical recovery of patients with COVID-19. More trials and meta-analyses are needed to assess the efficacy of inhaled corticosteroids for COVID-19 treatment.