evolutionary ceiling¶

The idea of an "evolutionary ceiling" is bunk science mixed with wishful thinking. In a sufficiently large population (say, billions of infections, each hosting trillions of viral genomes), there is virtually no opportunity for full fixation of an allele. Variation is preserved. https://t.co/Y8WVK5tqWB Any time there's a combination of mutations that confers increased fitness for the virus, by the time it has become the dominant strain, many new mutations have racked up. Even if it were to conquer the entire population, it has already diverged in the course of doing so. That was the original course of the virus, leading to the emergence of alpha, beta, delta, and omicron lineages as it spread. The omicron lineage eventually followed the same pattern, diverging as it took over the world to give rise to all its lineages that are now circulating. So far, none of the omicron sublineages has been able to completely overwhelm the others to repeat the cycle, because the relative fitness advantage of each particular set of mutations isn't enough to create directional selection. Instead, we get maintained polymorphism. Just like in the human population--where specific hair color doesn't confer a distinct advantage, so variation is maintained--in SARS-CoV-2, all you need is the ability to evade immunity--which is already an omnipresent feature of these various lineages. All of them can evade immunity to each other much better than evade immunity to themselves (as much as it exists), meaning the relative fitness of a particular set of mutations actually decreases as its frequency increases. This leads to stable polymorphism. At any time, a set of mutations could confer such a drastic fitness advantage for a lineage that it is able to overwhelm all the others and again upset the allele frequency balance. At this point, it will again spread rapidly, diverging into new lineages, and repeat the cycle. There is no herd immunity. There is no evolutionary ceiling. There is no mild strain. There is only prevention. And that prevention needs to be TOTAL, or this will keep happening forever.