We found very low-certainty evidence that wearing a face mask is owned by decreased probability of primary infection in RCTs as well as in observational studies. However, the wide confidence intervals affected the statistical significance with the overall estimate. It was not possible to create the certainty of evidence about mortality, filtering capacity and R0 whereas viral load was judged to become of very low quality. Our findings indicate (i) an over-all consensus toward a lowering of deaths, depending on prediction modeling studies, when the population mask coverage is near-universal, regardless of mask efficacy; (ii) filtration efficiency is dependent upon the face mask materials, with studies showing high variability.
It seems that all sorts of masks slow up the viral exposure, although numbers of protection, regarding reduction of inclination towards infection in the wearer, are usually lower for many materials (i.e., cloth masks), for the extent that they don’t effectively protect against infectious aerosols. Specifically, personal respirators were extremely effective than surgical masks, which are more efficient than home-made masks; (iii) in the worst-case scenario which has a mask efficacy at 30% plus a population coverage at 20%, the R0 reduced through the initial value of 2.0 to just 1.9; whereas within the best-case scenario, if the mask efficacy is 95%, the R0 can fall to 0.99 from a preliminary valuation on 16.90, even though no population coverage nor time horizon is reported; (iv) wearing vs. not wearing a mask is a member of a lowering of viral load of RR 0.25 (95% CI 0.09–0.67, determined by one experimental laboratory study).
Overall, our findings keep the recommendation on using goggles in community settings in a very pandemic era: home-made masks, like those created from teacloths, may confer a tremendous level of protection, albeit lagging than surgical masks or N95 personal respirators. Mask efficacy at 95% (N95 personal respirators) is apparently the best scenario, but it’s hard to realize in terms of adherence and charges from the public health perspective. A balanced compromise in the neighborhood might be reached with good population coverage using surgical masks (whose mask efficacy is >95%), which can be easier to implement. Comparing surgical masks to no mask indicates a viral load lowering of 1 / 4 (risk difference: 324 fewer × 1,000).