protective effect of masks and respirators against clinical respiratory illness (CRI)
(risk ratio [RR] = 0.59; 95% confidence interval [CI]:0.46–0.77) and influenza-like
illness (ILI) (RR = 0.34; 95% CI:0.14–0.82). Compared to masks, N95 respirators
conferred superior protection against CRI (RR = 0.47; 95% CI: 0.36–0.62) and
laboratory-confirmed bacterial (RR = 0.46; 95% CI: 0.34–0.62), but not viral infections
or ILI. Meta-analysis of observational studies provided evidence of a protective effect
of masks (OR = 0.13; 95% CI: 0.03–0.62) and respirators (OR = 0.12; 95% CI: 0.06–0.26)
against severe acute respiratory syndrome (SARS).
https://academic.oup.com/cid/article/65/11/1934/4068747