To evaluate the efficacy of N95 respirators and medical masks for protection against respiratory infectious diseases, including COVID-19. We conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) and observational studies evaluating the use of N95 respirators and medical masks for protection against respiratory infectious diseases. We retrieved relevant articles published from January 1994 to January 2020 by searching the PubMed, EMBASE, Cochrane CENTRAL, and Web

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... of Science databases. The study quality was evaluated using the Cochrane Risk of Bias tool with RevMan 5.3 software. Eleven RCTs adjusted for clustering were included in the meta-analysis. Compared with the control group, N95 respirators or medical masks conferred significant protection against respiratory infectious diseases (odds ratio (OR) = 0.50; 95% CI: 0.29–0.84). Compared to medical masks, N95 respirators conferred significant protection against respiratory infectious diseases (OR = 0.75; 95% confidence interval (CI): 0.57–0.99). Meta-analysis of 10 observational studies adjusting for clustering also suggested that N95 respirators and medical masks are effective for protection against respiratory infectious diseases (OR = 0.59; 95% CI: 0.42–0.82). However, only one case report showed the effectiveness of medical masks for preventing COVID-19. Although medical masks and N95 respirators may confer significant protection against respiratory infectious diseases, there is insufficient evidence to conclude that these types of personal protective equipment offer similar protection against COVID-19. Therefore, in the absence of sufficient resources during an epidemic, medical masks and N95 respirators should be reserved for high-risk, aerosol-generating producing procedures.