Studies range in effect sizes, but all the ones I read in March 2020 showed significant reductions in flu infection rates with masks. There were nice studies on cloth versus surgical versus N95 at the time too (summary: surgical and N95 were similar in performance, and much better than cloth, when used without full hazmat).
We know a lot more, specific to COVID, today. But that was best available evidence in March.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3591312/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5153448/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4699551/
Etc.
Studies range in effect sizes, but all the ones I read in March 2020 showed significant reductions in flu infection rates with masks. There were nice studies on cloth versus surgical versus N95 at the time too (summary: surgical and N95 were similar in performance, and much better than cloth, when used without full hazmat).
We know a lot more, specific to COVID, today. But that was best available evidence in March.