Surgical masks are not effective at preventing infection. They are effective at spreading infection.

New data on asymptomatic spreaders means than public health authorities are considering changing their advice. The default assumption would then be that everyone has it, and should therefore wear a mask to prevent spreading it.

This is a common misconception, for which CDC is also partially the one to be blamed.

Laboratory tests find that improvised cloth masks block 60 – 80% of virus particles

Most experts in the early 2000s agreed that these masks were probably better than nothing.

https://bmjopen.bmj.com/content/bmjopen/5/4/e006577.full.pdf

https://www.cambridge.org/core/services/aop-cambridge-core/c...

http://akkie.mods.jp/2019-nCoV/images/c/c0/%E3%82%B5%E3%83%B...

How many virus particles do you need to become infected? Is 20% of the load in a typical aerosol droplet from an asymptomatic infected person above or below that critical number?

>higher viral loads associated with severe clinical outcomes

Actually, they very much are.

1. Regular old surgical masks (not N95 respirators), when worn by the public without training, had a strong protective effect for the people wearing them during the SARS-CoV-1 outbreak. They reduced the risk of infection by ~70%. (Source: https://wwwnc.cdc.gov/eid/article/10/2/03-0730_article) The CDC even coauthored this one.

2. Despite being very different in their ability to actually filter out fine particles, N95 respirators and surgical masks actually show no significant difference in their ability to prevent diagnosed respiratory infections including influenza, when worn by healthcare workers according to two large meta-studies. Though both had a protective effect over no mask. (Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4868605/) (2nd source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5779801/)

3. When infected people wear a mask, it does help reduce the amount of viral shedding which occurs, presumably making them less likely to infect others. (Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3591312/)

In fact, if you dig into the research evaluating different mask types including homemade masks, one of them suggests that the masks are actually MORE protective on the way in than they are in preventing shedding of aerosols: (Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2440799/) (2nd source: https://www.researchgate.net/publication/258525804_Testing_t...)