Surgical masks and N95 respirators are not effective at preventing the flu. Of the 446 nurses who took part in this study, nearly one in four (24%) in the surgical mask group still got the flu as did 23% of those who wore the N95 respirator.
Influenza infection occurred in 50 nurses (23.6%) in the surgical mask group and in 48 (22.9%) in the N95 respirator group (absolute risk difference, −0.73%; 95% CI, −8.8% to 7.3%; P = .86), the lower confidence limit being inside the noninferiority limit of −9%.