[BostonCard]

The evidence is mixed at best.  Mechanistically, it should help.  I believe it probably does help.  However, viral transmission dynamics are complicated.  For example, this meta analysis suggests that it doesn't help to prevent influenza transmission:

https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article

Although mechanistic studies support the potential effect of hand hygiene or face masks, evidence from 14 randomized controlled trials of these measures did not support a substantial effect on transmission of laboratory-confirmed influenza. We similarly found limited evidence on the effectiveness of improved hygiene and environmental cleaning.

Here's the figure looking at the effect of the various studies in the meta-analysis:



Note that it also finds no support of a substantial effect of hand hygiene, even though it is widely accepted.  I think this paragraph from the discussion is most relevant:

It is essential to note that the mechanisms of person-to-person transmission in the community have not been fully determined. Controversy remains over the role of transmission through fine-particle aerosols (3,46). Transmission by indirect contact requires transfer of viable virus from respiratory mucosa onto hands and other surfaces, survival on those surfaces, and successful inoculation into the respiratory mucosa of another person. All of these components of the transmission route have not been studied extensively. The impact of environmental factors, such as temperature and humidity, on influenza transmission is also uncertain (47). These uncertainties over basic transmission modes and mechanisms hinder the optimization of control measures.

As I mentioned, this is a low-cost, low-risk intervention, so I am not against implementation, and use masks myself in cases where social distancing is not possible.  But we should also be honest about the uncertainties.  We don't know that it will work, and even if it does make a difference, it might not be as dramatic as some people think it will be.

I am just naturally cynical against any measure that is advocated as a "magic bullet" (not saying that you are making that assertion).  Experience has shown me that these are few and far between.  Usually, a long slog of small, incremental improvements are needed, rather than a single intervention.

BC

[BostonCard]

The evidence is mixed at best.  Mechanistically, it should help.  I believe it probably does help.  However, viral transmission dynamics are complicated.  For example, this meta analysis suggests that it doesn't help to prevent influenza transmission:

https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article

Although mechanistic studies support the potential effect of hand hygiene or face masks, evidence from 14 randomized controlled trials of these measures did not support a substantial effect on transmission of laboratory-confirmed influenza. We similarly found limited evidence on the effectiveness of improved hygiene and environmental cleaning.

Here's the figure looking at the effect of the various studies in the meta-analysis:



Note that it also finds no support of a substantial effect of hand hygiene, even though it is widely accepted.  I think this paragraph from the discussion is most relevant:

It is essential to note that the mechanisms of person-to-person transmission in the community have not been fully determined. Controversy remains over the role of transmission through fine-particle aerosols (3,46). Transmission by indirect contact requires transfer of viable virus from respiratory mucosa onto hands and other surfaces, survival on those surfaces, and successful inoculation into the respiratory mucosa of another person. All of these components of the transmission route have not been studied extensively. The impact of environmental factors, such as temperature and humidity, on influenza transmission is also uncertain (47). These uncertainties over basic transmission modes and mechanisms hinder the optimization of control measures.

As I mentioned, this is a low-cost, low-risk intervention, so I am not against implementation, and use masks myself in cases where social distancing is not possible.  But we should also be honest about the uncertainties.  We don't know that it will work, and even if it does make a difference, it might not be as dramatic as some people think it will be.

I am just naturally cynical against any measure that is advocated as a "magic bullet" (not saying that you are making that assertion).  Experience has shown me that these are few and far between.  Usually, a long slog of small, incremental improvements are needed, rather than a single intervention.

BC