Two independent reviewers appraised the potential risk of bias

There is a need to understand how masks can be used the whole day, by both children (at school) (50) and adults (at the office). In a study with the effect of mask use on household transmission of SARS-CoV-2, masks were found being successful, including for youngsters, and also the secondary attack rate for kids was discovered to get only half those of adults. However, the impact of masks on children has not been in comparison to adults (10). Some researchers have proposed that face shields could be appropriate in some environments (132), but it will not be well studied. Research on the efficacy of face shields, including in combination with masks, should be used, as well as research in to the efficacy of masks with transparent windows to the mouth.

face mask

Anfinrud et al. (59) used laser light scattering to sensitively detect the emission of particles of assorted sizes (including aerosols) while speaking. Their analysis established that visible particles “expelled” in a very forward direction which has a homemade mask consisting of a washcloth placed on two rubber bands round the head remained near background levels inside a laser scattering chamber, while significant levels were expelled when speaking with no mask.

When her Danish colleagues first suggested distributing protective cloth face mask to individuals in Guinea-Bissau to stem the spread in the coronavirus, Christine Benn wasn’t so sure. That was in March. But by July, Benn and her team had exercised the way to possibly provide some needed data on masks, and hopefully help people in Guinea-Bissau.


In case of disagreement, a third reviewer was consulted. We used the Cochrane risk of bias tool for randomized controlled trials (27); the Newcastle Ottawa scale for non-randomized studies (28). We planned to use the PROBAST (Prediction model Risk Of Bias Assessment Tool) for Prediction Model Studies (29). However, since we found only quantitative-deterministic models, (statistical) bias wasn’t the right measure of model goodness and we analyzed the QUAntitative-Deterministic models Risk of Infeasibility Assessment Checklist (QUADRIAC) in line with the appropriate guideline (30). We provided additional information in Supplementary Appendix 2.