a persistent myth¶

There seems to be a persistent myth (esp. among better-informed folks) that COVID will inevitably evolve to become lower impact. The idea is that the virus "wants" to trade lethality for infectiousness, since dead hosts can't spread it.

Unfortunately, this is not the case. We've known for a long time that you can spread COVID while asymptomatic. In fact, your highest level of infectiousness is just before symptoms show up (if they ever do). You can also spread COVID even if you never develop symptoms! In viruses, just like everything else with genetic material, mutations naturally occur every time that genetic material is replicated, which can affect their traits. Most do nothing, some kill the virus, some make it more or less infectious, some make it more or less lethal. Evolution works through selective pressure: if the environment of the population that is evolving makes it harder for some individuals to replicate and easier for others, based on those different traits, you'll inevitably see more individuals with the "better" traits. In the case of this virus, that environment is both the host it is currently infecting and all the people around it that it wants to infect. So traits that make a virus more able to spread inside a host are selected for, as well as traits that help it spread from host to host. In some viruses, there is actually a trade-off, because hosts fighting off a rapidly spreading infection tend to feel weak, avoid other people, etc. But COVID has a secret weapon: it can spread pretty far without triggering symptoms. The reasons for this are really complicated, and we don't have a complete picture. But put simply, the virus can infect the cells your body uses to kickstart the immune response (read: symptoms), slowing them down a lot. This lets the virus spread before you know it's there. That means there is no selective pressure against the virus spreading rapidly within a host, since it can do so without triggering symptoms that might hamper its ability to find new hosts. It's theorized that this initial spread impacts the eventual severity of the disease. Omicron is an example of a bunch of mutations that make it able to spread from host to host (even if the hosts have some prior immunity) and mutations that seem to make it less lethal. However, this is happenstance: a viral lineage that happened to evolve both sets of mutations. There's no reason to believe that future variants have to balance infectiousness against lethality. In fact, it is absolutely possible that both can be selected for, assuming that that initial pre-symptomatic stage does turn out to impact disease outcome.