I find myself repeating some background on COVID-19 to a lot of patients; some very basic information seems to not have made it to popular media. I’ll add my 2¢:

it’s not “zoo noses”

COVID-19 is what is called a “zoonotic” infection (a zoonosis, plural zoonoses). That’s zo-oh-notic. The root is “zoo,” and it means the pathogen (the SARS-CoV-2 virus in this case) had a stable animal reservoir where it was being passed around amongst the members of a community of bats (or possibly pangolins, or maybe both). When certain conditions were met, the pathogen jumped to a different host: humans.

This sort of thing happens all the time. Usually, nobody even notices: the pathogen doesn’t cause significant disease in the new host, or doesn’t live long, or cannot be transmitted. Often enough, though, the pathogen will cause severe disease in this new, accidental host. That’s when we take notice. “Bird” flu, “swine” flu, HIV, and many other zoonotic infections have become notable over the years.

We tend to think of viruses as malevolent little bugs whose desire is to do as much damage as possible. This isn’t the case, though. A virus doesn’t have a brain or any “desire,” it simply succeeds when it is able to reproduce in as many hosts as possible. So the evolutionary pressure on the virus is not to kill its hosts. Ideally, it wants its hosts running around being gregarious with other potential hosts (your friends), perhaps causing a little runny or itchy nose or such.

That evolutionary pressure is relentless, and it always wins. So while most questions about SARS-CoV-2 (how long will the pandemic last? will I be immune if I recover? will we find a cure/vaccine?…) can only reasonably be answered (so far) with “we don’t know,” we can say one thing for certain: over time, SARS-CoV-2 will mutate into less and less virulent (disease-causing) forms. The less virulent forms will crowd out the more virulent ones, and it will become less and less common for a SARS-CoV-2 infection to actually lead to a case of COVID-19, let alone a case requiring hospitalization or ventilation or leading to death.

how long?

The question is, how long will this take? We don’t know, but there are good reasons to be optimistic that it will be sooner rather than later. SARS-CoV-2 is a coronavirus, as I’m sure everybody now knows. But what does that mean? Well, coronaviruses are quite common, and probably account for about 40% of common colds. Yes, you have already had a coronavirus infection in your life (probably many!) and have recovered unscathed. So why aren’t you immune? Because coronaviruses mutate quite rapidly and tend to express surface proteins that change all the time, so that the virus that gave you a cold in March will look different to your immune system in May. That’s the reason that, despite decades of effort, we don’t have a “common cold shot” analogous to the “flu shot” influenza vaccine (and why personally I’m not banking on us developing a SARS-CoV-2 vaccine any time soon, though there are some tricks that might work for this specific coronavirus).

That rapid mutation rate has a silver lining, though. While it takes a zoonotic influenza virus a few years to become less virulent in the human population, the rapid mutation rate of coronaviruses means that they are likely to lose their virulence much more rapidly.

There is some intriguing evidence that this might already be happening. First, there was the series of 215 women admitted to labor and delivery at a New York City hospital who were all tested for SARS-CoV-2 infection. Eighty-eight percent of those who tested positive had no symptoms whatsoever, either at admission or at discharge a few days later. So they had the virus, and presumably were contagious, but never had any symptoms. Then the Los Angeles County Department of Public Health tested a large number of Angelenos picked more-or-less at random, and determined that the rate of infection in the community was 28–55 times higher than the number of tested and confirmed cases.

It could be that we would have found those numbers long ago if we hadn’t irrationally insisted on only testing people with a certain specific symptom complex, but I think it’s likely that what we are seeing is a growing reservoir of people with a much less virulent form of the virus. It could already be on the way out.