Twenty-one studies were included in the review (n=4,013, sample size range one to 2,200): six case series, five case controls, four cross-sectional, three case reports, two time series and one cohort control. No formal quality assessment details or summary scores were reported.
The authors stated that three studies directly compared the protective value of N95 masks with surgical masks. However, results from these studies were not clearly reported. Other results pertaining to the effectiveness of individual masks were reported in the paper.