[en-us]

I have been asking myself the same question. I think it comes down to two reasons:

1. Masks are in short supply and they believed they could save them for healthcare workers by convincing the general population they don't work.

2. If you are measuring efficacy, the general population won't reach the same level as a healthcare worker because they have not been professionally fitted and trained in on/off procedures. So instead of reducing risk by 95% the average person would see something like a 70% reduction, and they decided "perfect is better than good enough".

[tylerhou]

Nobody said that they don't work. But they are not effective for the average person because a month ago there were so few confirmed cases in the US that it would be extremely unlikely that you would ever encounter a COVID positive person.

On the other hand, healthcare professionals have to deal with infected patients all day. Suppose a mask is 95% effective on a healthcare professional, and 90% effective on a normal person. But the healthcare professional is in close proximity to a coronavirus patient nearly all the time. Without a mask, there might be 20 chances of infection every day for them. A mask would prevent 19 chances of infection.

For a normal person, they might encounter one CoV positive person per day. That means that a mask prevents 0.9 chances of infection. This is much lower than 19.

This math is off because I didn't account for mask changings, etc. A healthcare worker should change their mask more frequently than a layperson. After accounting for mask changes, though, I'm sure that the healthcare workers still get more benefit.

[Symmetry]

If they say "Masks work" when it only works 70% of the time then a lot of people will get sick despite wearing masks, there'll be a big public outcry, and people won't trust the WHO in the future.

[mnm1]

Maybe. Or they can just lose all trust instantly by claiming like the CDC, that they don't work. Now people who think will never trust the CDC ever again. Not sure what the WHO's wording was, but any organization not encouraging mass mask use cannot be trusted by anyone with a brain. Just because something isn't 100% effective, doesn't mean it's not effective. Only children and idiots think so. Unfortunately, we're surrounded by idiots.

[xorfish]

It would certainly be a failure if it is communicated that mask wearing prevents you from getting infected. They reduce the risk of infecting others more than they reduce the risk of getting infected.

A 20% reduction in infection risk is already substantial and worth it. If there is a 50% reduction in infecting others, mask use alone could replace most social distancing measures.

[en-us]

As opposed to public outcry from them saying masks don't work while countries with mask usage fare better?