The more times a theory holds up to being tested, the more confident we can be that the theory is truth, but it's never really 100% proven. Science encourages continuous testing and questioning of everything, and occasionally things long believed to be true turn out to be incorrect.
Just to add, often people will constantly raise the bar for "proof" if they don't believe in a finding, or lower the bar to ridiculousness if they want something to be true. Because you cannot really prove a negative, cognitive bias skews peoples views on what constitutes evidence so if a study is negative - it just wasn't precise enough, or wasn't large enough. If its positive - no matter how small or poorly designed - it must prove my theory right! Case in point the whole silly hydroxychloroquine/ivermectin debacle - where people are still quoting obviously fake studies.
Face masks are another one. The evidence now points in the direction they're completely ineffective, yet many still hold onto bad studies which state otherwise. Heck I was one of those who thought they were effective, yet my opinion has changed, in light of new evidence.
The evidence doesn't point in that direction at all. Sources?
The evidence definitely points in that direction, see
DOI: 10.1111/jebm.12424. Specifically, cloth and surgical masks are ineffective in stopping SARS-Cov-2 transmission. (This is a meta-analysis, combining the results of 12 studies, only one of which showed any benefit from cloth or surgical masks.)
Edit: It was pointed to me in a PM that I am be mischaracterising the conclusions of that study. True; their results were summarized as
"Fourteen studies were included in this study. One preclinical and 1 observational cohort clinical study found significant benefit of masks in limiting SARS-CoV-2 transmission. Eleven RCTs in a meta-analysis studying other respiratory illnesses found no significant benefit of masks (±hand hygiene) for influenza-like-illness symptoms nor laboratory confirmed viruses. One RCT found a significant benefit of surgical masks compared with cloth masks." with their conclusions (which sound odd to me, more like someone wishing for more research funding),
"There is limited available preclinical and clinical evidence for face mask benefit in SARS-CoV-2. RCT evidence for other respiratory viral illnesses shows no significant benefit of masks in limiting transmission but is of poor quality and not SARS-CoV-2 specific. There is an urgent need for evidence from randomized controlled trials to investigate the efficacy of surgical and cloth masks on transmission of SARS-CoV-2 and user reported outcomes such as comfort and compliance."Addendum: One of the most cited articles on the efficacy of cloth and surgical masks wrt. seasonal influenza, including coronaviruses but not explicitly SARS-CoV-2 (because the article is from 2011),
DOI: 10.1093/infdis/jir238 (
cited 72 times), showed that cloth and surgical masks are rather inefficient in preventing transmission; that basically, N95 (FFP2 in Europe) and eye protection is needed to prevent transmission of such viruses. It is a clearly written article, so I do recommend everyone interested in the subject read it.
In any case, regardless of the two studies above, looking at e.g.
NIH PubMed for 'sars-cov-2' and 'mask', the conclusions are best summarized as being from
"face masks could
help reduce transmissions" to
"there is very little evidence to support that face masks reduce SARS-CoV-2 transmission". But again, do feel free to check.
My point is that what evidence there is, points that cloth and surgical masks have not shown to be effective, only inconclusive or having little to no effect; whereas consistent hand hygiene (in earlier studies), N95/FFP2 masks when correctly worn and eye protection, do seem to provide significant protection. (But seeing how the majority cannot even seem to be able to correctly wear surgical masks, widespread
correct use of N95/FFP2 masks is unrealistic.)