1) Masks work. Even home-made ones provide some protection. Home-made ones are better for you to use because it frees up the good stuff for medical personnel, who are putting themselves in danger for lack of basic equipment. I have no idea why the WHO and other organisations insisted for so long that masks did no good. When this is over, these and other awful bureaucratic bungles will have cost thousands of lives at a bare minimum. [Edited to add: don't take more risks because you are wearing a mask or it could be worse than doing nothing. And learn how to use, take off & dispose of them]
2) While there's been lots of doubts raised about China's numbers, deaths in France & Italy are substantially underreported. If you didn't die in a hospital, it wasn't COVID according to official counts. There's also credible reporting that the situation in Japan is far worse than documented. Data biases such as these are a huge problem as we try to predict what's going to happen.
3) A large but uncertain proportion of cases are asymptomatic. I don't think there's a consensus yet, but I've encountered estimates ranging from 8% to nearly 90% (don't assume the average of those two is the best estimate). So even if you and the people you know don't feel ill, y'all could carry the virus. Just stay home. [Edit: newer evidence points towards less than 50% being asymptomatic]
4) Relatedly, it's possible that the number of infected people is a lot higher than we thought, because the other numbers that we have (R0 & date of start, for example) don't entirely make sense together. If so, it would imply that the death rate is lower than we thought. We don't have enough random testing to figure this out yet.
5) Differences in death rates between countries continues to be hard to explain. For e.g. Germany's extremely low death rates are still not well-understood. They have been testing a lot, but it's still a bit surprising. Lots of ideas are being explored, from demographics, social practices, smoking, and weather, to weirder ones like whether the country mandated BCG vaccination (having a bacterial vaccine protect against a new virus would be weird, but it's apparently a serious idea). So far it's all quite speculative.
6) We've ramped up testing in the last 2 weeks but are still testing far less than we should. And yet we've wasted more than a month not trying pooled testing i.e. putting samples from many people and testing them all together. If it comes out positive, at least one of the people from the set has it. All can be quarantined till more information is available. This simple idea might have saved a lot of lives.
7) Other old or outdated ideas that may become valuable now: using plasma from recovered patients to help treat patients (carries antibodies), and variolation (an ancient form of vaccination).
8) Contact tracing continues to be a really, really important follow-up. Despite hundreds of billions of dollars being deployed towards helping people and companies worldwide, little of this money is being directed towards ramping up testing and tracing, which is bizarre. We may need to do this kind of tracing for months to years.
9) Once you've recovered, most experts seem to think you'll be immune, at least for a while. These recovered people are going to be really, really important in getting a country back on its feet. When a country is shut down, it's not just money that is lost - lives are too. Especially in poorer countries i.e. where most of the people are. Germany is planning on making best use of recovered people by issuing them documents that could perhaps enable fewer restrictions on travel and work. Other countries will hopefully do this too.
10) Many countries are understandably banning export of important medical equipment and medicines. But everyone is going to suffer as a result. As medical supply chains get decimated, every country loses access to important components from these bans.
11) In the coming months, if millions do not die, you're going to hear a lot about how we overreacted, and the epidemiological modelling community in particular is going to come under attack. Prepare to fight these smears. This is an incredibly difficult job being done under a huge cloud of uncertainty, and counterfactuals are hard. If they do their job well and their advice is followed, the direst predictions will not come to pass. Proving them wrong by taking strong action is success and we should celebrate it. This does not mean these models are immune to criticism - there has already been strong, fast and justifiable criticism of some that have been published.
12) There's a huge number of volunteer efforts offline and online, and you don't need any particular expertise to be useful. If you feel up to it, you can join the fray. Ping me if you want suggestions.
Take care of yourselves, your productivity is probably not as important as it seems right now. We're in this for the long haul.
IMPORTANT: if you think any of these are wrong or questionable, please let me know! This is a fast-moving topic and I'd like to be accurate.
In response to a question about the effectiveness of masks:
I agree that wearing a mask will help a lot less and might even be worse than nothing if it means that you (1) touch your face more, or (2) do riskier activities that you would without a mask. I think the solution to this is education, not dissuading people from using masks, just as we don't dissuade people from using seat belts because they might drive more riskily.
My take-aways from the general reading listed below are: (1) masks are considerably better than nothing; home-made masks are far from perfect but provide some protection. (2) they probably reduce viral load in transmission, and it seems like that may be important, (3) they are even more important in protecting the public from the infected (whether symptomatic or not) than in protecting the individual wearer, (4) despite these limitations, they can be really important because they can help reduce the rapid growth/spread. In other words, if you care about the population level, it helps to reduce average individual risk by even a little.
Regarding reading, this is the most balanced (non-peer reviewed) piece I've read, by a doctor who summarises the literature. He's a reliable writer.
To summarise a couple of papers (some of which are mentioned in the slatestarcodex piece):
This big review finds mixed evidence but if you peer closely, it's generally in the direction of helping (reviewed well in the piece above) and their conclusions seem too conservative given the present situation:
This paper found that masks - including cloth ones - reduced aerosol exposure.
This one found that surgical masks provide some imperfect protection against aerosolized flu virus (viral load reduced by a factor of 6 on average):
This one shows that normal cloth masks can filter out ~50%-70% of a small virus:
This comparison study based on people who did and did not get SARS has problems but suggests that masks helped to protect:
Here's a compilation of more papers and a summary of the arguments, though I can't vouch for how reliable/unbiased the author is:
Two additional points. The fact that all the organisations that do not recommend masks in general do recommend them for infected people and for caregivers is clear evidence that they too believe that masks work. And the few countries that have normalised mass use of masks are doing relatively well. The comparison with East Asian countries is challenging because there are many differences between those countries and Europe/the US. But the Czech republic has also done pretty well in recent weeks after mandating mask use (note: I have not investigated this particular point carefully, so my confidence in that story is not very high yet).
In response to a comment about masks mentioning this paper:
There's two comparisons to think about here. The paper you link to compares cloth masks with medical masks and finds "the results caution against the use of cloth masks".
The result makes complete sense to me, but the conclusion is too broad. Because right now the comparison I and many other people are interested in is not cloth masks vs. medical masks, but cloth masks vs. no masks. And I contend that the evidence supports cloth masks if the alternative is no mask at all. I've posted a few relevant links in my response to the previous question. Additionally, if the public uses cloth masks, they both reduce their risks and make more of the good masks available to medical personnel, which is very, very important.
Of course, people should definitely not take additional risks because they have protection. Everyone should still be staying home.