TL;DR; N95 vs surgical masks - too close to call. 48/221 N95 vs 50/225 surgical mask got the flu.
https://pubmed.ncbi.nlm.nih.gov/19797474/
"Context: Data about the effectiveness of the surgical mask compared with the N95 respirator for protecting health care workers against influenza are sparse. Given the likelihood that N95 respirators will be in short supply during a pandemic and not available in many countries, knowing the effectiveness of the surgical mask is of public health importance."
...
Results: Between September 23, 2008, and December 8, 2008, 478 nurses were assessed for eligibility and 446 nurses were enrolled and randomly assigned the intervention; 225 were allocated to receive surgical masks and 221 to N95 respirators. Influenza infection occurred in 50 nurses (23.6%) in the surgical mask group and in 48 (22.9%) in the N95 respirator group (absolute risk difference, -0.73%; 95% CI, -8.8% to 7.3%; P = .86), the lower confidence limit being inside the noninferiority limit of -9%.
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https://pubmed.ncbi.nlm.nih.gov/31479137/
"Conclusions and relevance: Among outpatient health care personnel, N95 respirators vs medical masks as worn by participants in this trial resulted in no significant difference in the incidence of laboratory-confirmed influenza."
https://pubmed.ncbi.nlm.nih.gov/19216002/
"Conclusion: Face mask use in health care workers has not been demonstrated to provide benefit in terms of cold symptoms or getting colds. A larger study is needed to definitively establish noninferiority of no mask use."
"The researchers found that when people and their families wore face masks and washed their hands within 36 hours of the first symptoms, their family members were less likely to become infected. However, those who started using masks or washing their hands after the 36-hour time period had passed saw no benefit.
In tandem with hand-washing, face masks seem to work better than hand-washing alone, but the authors could not conclusively prove which intervention was responsible for the drop in infections of family members."
...
"Currently, the Centers for Disease Control and Prevention, which partly funded the study, does not generally recommend the use of face masks or respirators to prevent the spread of H1N1 because of their uncertain benefit. The CDC says face masks are recommended only if a person is at a very high risk of flu complications (such as someone who is pregnant), and has no other choice but to be the primary caregiver for a family member with H1N1. (The CDC says this scenario should be avoided if at all possible.)"
https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article?fbclid=IwAR3ASxBUrRE5LHeZsZF-iHrpTuX2PprS8FnkKGUpEUDEIAnH6s5wQOpkOJI
"We did not find evidence that surgical-type face masks are effective in reducing laboratory-confirmed influenza transmission, either when worn by infected persons (source control) or by persons in the general community to reduce their susceptibility (Figure 2). However, as with hand hygiene, face masks might be able to reduce the transmission of other infections and therefore have value in an influenza pandemic when healthcare resources are stretched."
Result: Masks wearing benefits are not confirmed by this study.
https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article?fbclid=IwAR2V1hPqN0WKb2kXVExP_1UE9ARvru6mtPZvZN0w1jx0S3l3fXLhxMP_bXs
"In this review, we did not find evidence to support a protective effect of personal protective measures or environmental measures in reducing influenza transmission. Although these measures have mechanistic support based on our knowledge of how influenza is transmitted from person to person, randomized trials of hand hygiene and face masks have not demonstrated protection against laboratory-confirmed influenza, with 1 exception (18). We identified only 2 RCTs on environmental cleaning and no RCTs on cough etiquette."
"Hand hygiene is a widely used intervention and has been shown to effectively reduce the transmission of gastrointestinal infections and respiratory infections (26). However, in our systematic review, updating the findings of Wong et al. (8), we did not find evidence of a major effect of hand hygiene on laboratory-confirmed influenza virus transmission (Figure 1). Nevertheless, hand hygiene might be included in influenza pandemic plans as part of general hygiene and infection prevention."
TL;DR; N95 vs surgical masks - too close to call. 48/221 N95 vs 50/225 surgical mask got the flu. https://pubmed.ncbi.nlm.nih.gov/19797474/ "Context: Data about the effectiveness of the surgical mask compared with the N95 respirator for protecting health care workers against influenza are sparse. Given the likelihood that N95 respirators will be in short supply during a pandemic and not available in many countries, knowing the effectiveness of the surgical mask is of public health importance." ... Results: Between September 23, 2008, and December 8, 2008, 478 nurses were assessed for eligibility and 446 nurses were enrolled and randomly assigned the intervention; 225 were allocated to receive surgical masks and 221 to N95 respirators. Influenza infection occurred in 50 nurses (23.6%) in the surgical mask group and in 48 (22.9%) in the N95 respirator group (absolute risk difference, -0.73%; 95% CI, -8.8% to 7.3%; P = .86), the lower confidence limit being inside the noninferiority limit of -9%.
--
https://pubmed.ncbi.nlm.nih.gov/31479137/ "Conclusions and relevance: Among outpatient health care personnel, N95 respirators vs medical masks as worn by participants in this trial resulted in no significant difference in the incidence of laboratory-confirmed influenza."
https://pubmed.ncbi.nlm.nih.gov/19216002/ "Conclusion: Face mask use in health care workers has not been demonstrated to provide benefit in terms of cold symptoms or getting colds. A larger study is needed to definitively establish noninferiority of no mask use."
https://www.cnn.com/2009/HEALTH/08/03/face.mask.flu/index.html
References a study that concludes:
"The researchers found that when people and their families wore face masks and washed their hands within 36 hours of the first symptoms, their family members were less likely to become infected. However, those who started using masks or washing their hands after the 36-hour time period had passed saw no benefit.
In tandem with hand-washing, face masks seem to work better than hand-washing alone, but the authors could not conclusively prove which intervention was responsible for the drop in infections of family members." ...
"Currently, the Centers for Disease Control and Prevention, which partly funded the study, does not generally recommend the use of face masks or respirators to prevent the spread of H1N1 because of their uncertain benefit. The CDC says face masks are recommended only if a person is at a very high risk of flu complications (such as someone who is pregnant), and has no other choice but to be the primary caregiver for a family member with H1N1. (The CDC says this scenario should be avoided if at all possible.)"
https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article?fbclid=IwAR3ASxBUrRE5LHeZsZF-iHrpTuX2PprS8FnkKGUpEUDEIAnH6s5wQOpkOJI "We did not find evidence that surgical-type face masks are effective in reducing laboratory-confirmed influenza transmission, either when worn by infected persons (source control) or by persons in the general community to reduce their susceptibility (Figure 2). However, as with hand hygiene, face masks might be able to reduce the transmission of other infections and therefore have value in an influenza pandemic when healthcare resources are stretched." Result: Masks wearing benefits are not confirmed by this study.
https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article?fbclid=IwAR2V1hPqN0WKb2kXVExP_1UE9ARvru6mtPZvZN0w1jx0S3l3fXLhxMP_bXs "In this review, we did not find evidence to support a protective effect of personal protective measures or environmental measures in reducing influenza transmission. Although these measures have mechanistic support based on our knowledge of how influenza is transmitted from person to person, randomized trials of hand hygiene and face masks have not demonstrated protection against laboratory-confirmed influenza, with 1 exception (18). We identified only 2 RCTs on environmental cleaning and no RCTs on cough etiquette." "Hand hygiene is a widely used intervention and has been shown to effectively reduce the transmission of gastrointestinal infections and respiratory infections (26). However, in our systematic review, updating the findings of Wong et al. (8), we did not find evidence of a major effect of hand hygiene on laboratory-confirmed influenza virus transmission (Figure 1). Nevertheless, hand hygiene might be included in influenza pandemic plans as part of general hygiene and infection prevention."
Study on cloth masks -- tl;dr; Cloth mask is worse than no mask https://www.sciencedaily.com/releases/2015/04/150422121724.htm