Mike4 wrote:I hear it said once in a while that viruses as they mutate, tend to get more infectious and less dangerous. Is this correct in your opinion Hal?
That's one of those deceptively complicated questions. Anthropomorphising horribly, you have to remember that the virus doesn't really "care" what it does to people. All that matters is that it makes as much virus as possible, and there are various strategies to achieve that.
Infectivity is always good, so there's always a drive to become more infectious. But the best way to be infectious can vary. Delta is more infectious in most environments because it has more viral particles in the upper respiratory tract (RT). But you can imagine that in an environment of heavy testing of swabs of the upper RT, the best way for a virus to propagate might be to become more like B.1.616 which most PCR testing misses because it has almost no viral particles in the upper RT for most of the course of an infection.
And "less dangerous" is even more complicated. Killing a host quickly is almost always bad. But as long as the host lives for long enough to pass on the virus, the virus doesn't much care if the host dies later. Something like HIV is still "dangerous" even 40 years since it emerged in that it still kills untreated people pretty reliably - but not before a good long time for transmission.
The human body seems to be pretty good at clearing up respiratory infections within a week or two, so that's the main window for transmission and human respiratory viruses don't need to worry too much about what happens to their host after that window. So SARS2 is already about as "undangerous" as it needs to be, particularly since the people in developed countries who go on to die are generally ending up in a hospital, usually in intensive care where there's lots of precautions and not much scope for further transmission. That means there's not much pressure on it to become less "dangerous" than it already is and it might take decades to do so, driven by what happens in less-developed countries.
But then with such a small genome, there's always a risk that infectivity and lethality are linked, and if a mutation makes it much more transmissible but a little bit more lethal, then that mutation could still spread in the population.