1) I claimed in the last post that testing people for antibodies to check if they are immune will be very important in getting societies and economies back on track. However, I neglected one extremely important detail. Every test generates 'false positives' and 'false negatives'. Even values that can sound very good for the whole population (5% for false positive and false negative rate, for example) can provide very bad information for an individual. Suppose you get a positive test result; does that mean you have the antibodies? Well, it depends a lot on how common the antibodies are in the population tested. If the antibodies are present in only 1% of the population (roughly what we may expect for many countries now), then getting a positive result means only about a ~16% probability that you actually have the antibodies. This is a simple, profound, and deeply confusing result that is at the core of teaching the usefulness of Bayesian statistical thinking. So this strategy to open up societies slowly is going to be harder than I thought. If you're interested in the maths (it has major implications for disease testing too), you can read about it at https://betterexplained.com/.../an-intuitive-and-short.../
2) The viruses are spread through the air. This may seem somewhat obvious, but it was contradicted by many authorities based on a difference between the plain-English meaning of that sentence and a more arcane technical definition that hinged on differences between droplets that were bigger and smaller than 5 microns. Things have now been somewhat resolved by evidence that the viruses are spread through droplets smaller than 5 microns too, so the plain-English and technical definitions are in agreement. But this is bad news for us, because it means that the virus spreads even more easily than thought.
3) Related to the previous point: jogging, biking and other physical activity is great in general but probably not ideal right now if it brings you near other people. Especially because exercising makes you and your fellow joggers breathe more heavily, spreading the virus even further. How much could this kind of thing matter? We don't really know. But in one horrifying story, a choir of >100 completely asymptomatic people met to practice while maintaining distance from each other. Nearly half of them later fell ill with the virus. A somewhat extreme example because singing involves intentionally expelling air, but physical activity does have a similar effect.
4) Say you have to go out (for e.g. to get groceries) and you therefore cannot totally avoid people. Some reasonable advice I encountered: imagine that they are smoking/vaping and you are trying to avoid the plume from them. Think about how far smoke can travel too, and how it is affected by air movement.
5) A consensus seems to be building that the proportion of infected people who never show symptoms (i.e. asymptomatic) is less than 50%, possibly much less. This is lower than the estimates I wrote about last time. It is also bad news, because it means that there are many more people to infect and the death rate is higher than we hoped. So remember that even if you and a friend have no symptoms, you are at risk and putting them at risk if you are physically close to them.
6) Even if they do develop symptoms, people pass on viruses before the symptoms appear (roughly for a few days). If you've been exposed to someone who developed symptoms days later, you ought to be extra careful to not expose new people.
7) The number of viruses you get hit with is likely to be important. Which also seems somewhat obvious, but it has important implications. Even if you cannot eliminate all risk, anything that reduces the number of viruses you get exposed to helps. Which is one reason why imperfect barriers such as homemade masks might be useful for personal protection (NOTE: the main benefit of masks is that it prevents you from spreading the virus if you are carrying it). And yet another reason why it is imperative that medical personnel get the very best protection, since they are exposed both frequently and to very high numbers of the virus.
8) There's a lot of concern about the evolution of the virus among members of the public. Some people are concerned that it could become more deadly, and some with a bit of training in evolution think it will become less dangerous. We have no evidence for either of these ideas, and good reason to think that they are both wrong. (i) There's plenty of work been done to sequence versions of the virus isolated from people around the world, so we have lots of information about how it has mutated and spread. To our knowledge, none of these mutations has had any effect on how dangerous the virus is or its spread. Mutations happen randomly and many of them do essentially nothing. (ii) Some pathogens do in fact evolve to become less dangerous to their host, because if they kill their host too quickly, they are less successful at spreading. However, this virus spreads very successfully even before symptoms appear, kills a small percentage of hosts, takes a while to kill, and some people never develop symptoms at all. So it is less susceptible to that kind of evolutionary dynamic. Also, some diseases such as smallpox existed with humans for thousands of years and remained lethal throughout; so it's not wise to expect a few months of evolution to save us.
9) Related to this, when you hear discussion about new 'strains' of the virus, it is not necessarily cause for alarm. What constitutes a strain is a rather technical topic; just because a new strain is found does not mean that there are new or greater risks. Listen to whatever the virologists say about it.
10) Everyone is focussed on their own countries and this is natural. But if rich countries fight to retain protective equipment, it is going to be catastrophic for poor ones. Poor countries already have orders of magnitude fewer doctors and medical equipment. If these few doctors get only minimal supplies of protective equipment, it may lead to deaths on the scale of tens of millions (frankly, my mind can't comprehend losses on that scale so I can't even be confident it will not be worse). This needs a global response; I fear we are not up to it and the poor will suffer in a way we have not seen since...I don't know when really. Somebody more historically-minded can educate me.
11) India is one such poor country, and there's a special place in hell for members of this government, who took a system already completely unprepared and hammered it further by (i) choosing this moment to award a monopoly on protective equipment to one company that promptly raised all prices, and (ii) refusing for months to allow private companies to manufacture protective equipment that the hospitals desperately needed to stock up on. India is on a particularly bad path right now, with tens of millions walking home en masse without food or resources, the government hell-bent on ignoring evidence, suppressing a media that is mostly pliant anyway, and blaming outbreaks on individuals and Muslims. Meanwhile, they have no strategy in place beyond one terribly-planned lockdown, banging some pots and pans together, and recommending cow urine as a cure (to be perfectly fair, which it grits my teeth to do, the cow urine recommendation is not official and comes from a subset of the ruling party).
12) The limited reporting I've seen from developing countries is scary. The lack of cases seems far more likely to be from extremely bad testing than from success in containing the virus or luck in other ways (viral susceptibility to environmental conditions, for example). The wealthier countries are ramping up testing but I don't know to what extent this is true in the poorer ones. This is probably going to get a lot worse. We need international news agencies and organisations to shed more light on what is going on in these countries.