You're mainly taking offense with the lack of a citation, I think, but I might be able to at least explain the timeframe mentioned here. I'm neither a doctor nor working in this field, so take everything with a grain of salt:

The incubation period is usually five days or more, while patients can already be infectious two days before symptoms show. That means there is a window of opportunity of 2-3 days to find contacts of the current case and put them into quarantine before they start infecting even more people.

Where the percentage comes from, I do not know but I would assume that it is meant to push the number of new infections per case (R = reproduction number) to 1 or even better well below it (R < 1 means it would eventually fizzle out). Super sketchy math: if the reproduction number is ~2.5 and you trace and quarantine 90% of the contacts (1 - 0.9) * 2.5 ~= 0.25 new cases will slip through. They might be aiming at such a high number to compensate for other cases where no tracing is done (e.g. because it was not known that the patient was Covid-19 positive) to keep the overall reproduction number low.

Once again - I am not a professional and just offering some thoughts about the problem (and happy to be corrected / to learn more).

Did experts actually say masks were ineffective at reducing transmission?

I recall it was more about not buying up masks so that healthcare workers had enough. And that masks may not help stop contracting it oneself.

At the time the belief was that COVID spread largely through touching infected surfaces. That combined with the fact that there was a massive shortage of masks meant that they warned against using masks. Also, the role of asymptomatic carriers wasn’t all that clear.

And it was probably the right call based on the information we had then (the real question is what the US government was doing for the many months notice it had and why it did not use its powers to deploy companies to manufacture masks or as in the case of GM agree to pay the at cost rates they were offering the US government for manufacturing PPE and ventilators).

Once it became clear that asymptomatic carriers and spreaders existed, and that the majority of spread was through water droplets emitted during actions like speaking and singing (unlike most other viruses where it’s usually sneezing and coughing), the advice was changed rapidly since regular cloth masks could be effective for this purpose.

This wasn’t a failure of expertise but was the natural consequence of facing a novel threat that was moving faster than we were learning about it.

I recall articles saying that there's no point in lay folk wearing an mask. They're impossible to wear properly without four years of medical training, presumably mostly focused on mask wearing rather than silly things like anatomy, so anyone else wearing one is a complete waste. Leave it to the professionals.

I'm exaggerating but not by much...

Contrast with the current messaging. They work but are in short supply. If you have a stash of new surgical or N-95 masks, please donate it. If you have a used mask, please continue wearing it. You're encouraged to make, wear, and sell/give to anyone non-medical-grade reusable masks. Anything is better than nothing.

Those articles were almost certainly written by journalists who have no medical or epidemiological training.

As are essentially all news articles.

Unfortunately yes they did. Even in my hospital I remember when the recommendations were that masks were unnecessary unless in a covid room. I’ve been treating covid pts since April.

Edit: maybe for clarity I should add that I don’t remember anyone saying it was ineffective, just unnecessary. I witnessed several physicians wearing their own masks be told by higher ups to stop though. I’ll have to look through old emails, things have changed on a weekly basis.

I can't say for US, but yes, both WHO and local government health figures were spouting that masks don't work. LAter they recanted that the reason they said that was because there weren't enough, but the initial dialog was they were ineffective. (from a previous discussion, I think France was the same)

Their statements were worded to state they were probably ineffective for healthy people to wear for their own protection in the general environment. That is probably true in that the point of masks is mostly to protect others. So if you don't have enough masks (for total coverage,) a higher risk group using them all was not going to be effective in protecting the high risk individuals unless they tend to cluster.

Correct. It was always said if someone was sick they should wear a mask (more studies have come out confirming this). Once asymptomatic became such a big transmission vector it made sense for everyone to wear a mask. PPE was/is still an issue, so cloth masks were also questionable early on, but have since shown effectiveness.

https://jamanetwork.com/journals/jama/fullarticle/2768532

More precisely they stated that there were no studies proving effectiveness. They were hiding behind the scientific method to serve some other purpose.

I think the problem is rather that the public was looking for ideally easy and hopefully definitive answers and were confused when they saw scientific progress unfold in real time instead, with all uncertainties, theories and what it entails.

I definitely had a good share of discussions revolving around "scientists are saying different things every week" in the last few months. My closer connections seem to understand now.

The US Surgeon General went a step further and literally said "You can increase your risk of getting it by wearing a mask if you are not a health care provider"

This might be a garbled valid point?

Somewhere I read that among the reasons for ordinary people not to wear N95 masks is that the valve lets air out freely, while filtering incoming air. This would make you more likely to infect others if you are infected, than some other kind of mask.

It's not that you increase your own risk per se, but you increase the risk of your class, of civilians, by wearing it.

Not exactly-exactly.

N-95 masks can be with or without valves.

With the valve they are pointless if the werarer is positive/transmits the illness.

The valveless ones are fine, but both with valve and valveless are not as useful as they promise (filtering 95% or so) because the wearer must be trained to use them AND the masks need to be suitable to the wearer, after a proper "fit test" AND the wearer must be medically tested to be able to breath with reduced flow.

The exact method the fit test (and the medical check) is performed varies by country/norm, but check this:

https://www.osha.gov/video/respiratory_protection/fittesting...

https://www.youtube.com/watch?time_continue=559&v=D38BjgUdL5...

Basically you choose among 10-12 different models the one that seemingly fits better your face, then you put the mask on, a sort of transparent plastic hood is put over your head and a small quantity of substance is sprayed (usually vanilla or similar highly penetrating odour) under the hood, if you can smell it, the mask is not the proper fit or has not been put on properly and you start again.

Then, the particular model of mask with which you passed the test is "your" mask (and you won't use another model).

And of course you need to be cleanly shaved.

A "surgical mask" has a much lower filtering potential, but unlike the N-95 masks (FFP-2 in Europe) anyone can reach it without issues.

>N-95 masks can be with or without valves.

I didn't say they necessarily have valves, but all the ones I've seen do. I had one intended for painting, gave it to a local hospital.

The US Surgeon General is also a mouthpiece for the current administration.

I seem to recall Dr Fauci on 60 minutes saying they don't really work. That they might make you feel better for wearing one but also have unintended consequences because you're always fiddling with such a thing. So he wasn't suggesting people wear them at the time.

Randomly searched YT of what I'm referring to: https://www.youtube.com/watch?v=5gYAka7qSnM

More or less the message was, you don't need a mask because you shouldn't be out in public anyway.

Right, the abstinence-only approach. Which worked exactly as well as you'd expect.

Fauci said exactly that. He told the general public a lie because he was concerned that the health sector would not have enough masks.

He could have told everyone to wear bandanas or other homebrew mouth coverings but he did not.

Even though I would generally agree with you: what makes you think that Fauci and his colleagues did not simply not know that mask are as effective as we now know they are?

Fauci admitted on camera that he gave that advice because he was worried that medical staff would run into shortages.

I was not speculating in my comment, this is Fauci's own admission.

Source: https://www.thestreet.com/video/dr-fauci-masks-changing-dire...

Not exactly a citation[1], but this agent-based simulation suggest that mitigations like quarantine are highly sensitive to how thoroughly they are applied: https://www.youtube.com/watch?v=gxAaO2rsdIs

[1] I'm putting this firmly in the "all models are wrong, but some models are useful" camp