Let’s start with two words: “cases” and “infections” (i.e., infected persons) which media, and sometimes officials, are confusing (conflating.) As if these two numbers were the same.
Far from it. These two things are very, very different. A “case” is someone identified (and confirmed by DNA) as having the novel coronavirus 2019-nCoV by the medical system. Almost certainly, these individuals are showing symptoms (or deceased, of course.) As of this article there are a few thousand such cases, worldwide.
But there are at least ten thousand infected persons, probably far more, who have symptoms already but who don’t count as “cases” because they have been told not to come to a hospital in China, or been turned away and told to quarantine themselves, or are awaiting testing (since testing kits are in short supply at the epicenter, now.) Unless they die it’s very unlikely that those who are now isolating themselves at home will ever get tested to see what virus they had. Yes they have the 2019-nCoV illness, but they may never be “cases” of 2019-nCoV. This group is probably at least several times the official total of “cases.”
But we’re not done. Not nearly. To get to the number of “infected persons” we ALSO need to add in all those who are infected and will get symptoms in a few to fourteen days, but have not yet shown any symptoms. The number of these infected non-cases is likely another multiple of two or more of the total of symptomatic infected persons who are untested mentioned above.
But we’re STILL not done.
PLUS we need to add in all those patients who have been infected, but perhaps only with a few virus particles (as opposed to a droplet loaded with the virus) and whose bodies have silently fought off the infection. Either via their innate immune system, or adaptive immune system (in which latter case they’ll have antibodies that can be detected later.) With most infectious diseases, herd immunity is difficult to achieve without a lot of such infections. We haven’t any idea of how many of these infected persons are out there. Maybe another multiple of two. Maybe less. Maybe another multiple of several again! Or more!
If the latter figure for “infected persons” seems alarming, be of good cheer, because such a very high figure for “infected persons” would be very good news indeed. It would mean that most people won’t be harmed by this new illness or feel sick as a result of it, no matter what.
So please, official media, please stop saying cases when you mean infected persons and infected persons when you mean cases. It’s desperately misleading.
I know some people are going to question the possibility that there are, and have been, very large numbers of infected persons who will never show symptoms (or pass on the disease,) I’m sure. I should explain why that’s possible, particularly in this case.
Wholly asymptomatic cases of many diseases are common, but they may be more common when you’re dealing with a (very likely) zoonotic virus that’s just leapt over from an animal host and is just not very good at establishing itself in humans. A rather incompetent virus, as it were.
But don’t take that as a prediction about numbers. Zoonotic viruses are not predictable.
That’s because when a virus leaps species, you’re in a casino situation. Two complex systems that have never met, or not met for hundreds of years, are colliding. The virus may turn out (especially with an early mutation or two) to be pretty good at surviving inside a human body. More likely, it’s not all that great at surviving and multiplying in the new species. (In which case most people may not even notice when and if they get infected, because their immune system will be able to shrug it off. Infection yes, but no symptoms, no illness, and they don’t become carriers either.)
On the other hand, the ordinary human adaptive immune system may well be terrible at fighting the virus, too (or fairly good — it’s a casino situation.) Both of these conditions can happen together of course. That’s a combination that’s not, given that neither system has begun to adapt to the other.
It is also likely that there will be more variability in the competence of our immune response to novel zoonotic viruses, since the worst combinations of human immune factors (re fighting this specific virus) won’t yet have been weeded out.
Thus, paradoxically, a zoonotic virus can both have difficulty surviving in most people, at all, yet still kill far more of those humans it is able establish itself in than a flu would — because many human immune systems are even more incompetent at eliminating the virus, as well.
To give you just one example of media getting it all dead wrong, and this in an article trying to attack misinformation, no less:
“A viral post online claims the number of people affected by the coronavirus outbreak is close to 90,000 — significantly higher than numbers reported by officials.
Officials in China have reported the illness has killed at least 81 people, and infected more than 2,700 others.”
Obviously, the author (and their editor) had no idea that cases and infected persons were completely different things. Argh. I understand that journalism no longer pays and is now done in great haste, but Argh!!
Another couple of other misconceptions being spread by much of the media, and some officials as well:
R0 (which describes how infectious a disease is) is not a feature of the virus or even a fixed number (as the head of CDC seemed to believe in his news conference, today.) It’s a value describing what happens to a given virus in a given environment.
Change that environment (by everyone putting on googles as well as masks every time they go out, for example) and R0 can change too, often dramatically. This was shown in the case of SARS, re masks. Additionally, mutations that increase R0 (and reduce fatalities) are common, especially early in the history of a zoonotic virus.
It follows that the R0 in China (with masks everywhere) could be far lower than it will be in the U.S. if it arrives there, where masks are rarely seen, and sometimes ridiculed. Unless masks and googles become very popular, very quickly.
Lastly, most authorities seem to be succumbing to the fallacy of recency, and are optimistically comparing the novel coronavirus 2019-nCoV to SARS, to a greater degree than they should. This is poor logic. The viruses look similar, but much about the novel virus seems very different, including its asymtomatic spread. (Now shown by a German case of transmission.) That’s a very dramatic, and very sobering, difference that makes containing the virus at this point very unlikely (without a vaccine.) Apples and oranges.
For what it’s worth, studies show that experts are actually worse than the public at making predictions when talking about anything that’s just outside the range of their expertise. Matters that seem familiar, but really aren’t. Novel zoonotic viruses fit that bill pretty well, I would guess.