Is a mask necessary in the operating theatre?
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2493952/pdf/annrcse01509-0009.pdf
Judging from the articles cited, this was before the age of routine pre-op antibiotics.
And that study looked at, and the reason for surgeons wearing masks has always been, preventing BACTERIAL infection. Bacteria are much larger than viruses, and yet this study found no difference in bacterial infections when masks were not worn. If masks don’t stop bacteria then they most certainly have no effect on viruses. Wearing them to prevent COVID or any other viral infection is 100% a placebo.