Sort-of. But it is complicated.Fingal wrote: ↑Mon Mar 01, 2021 10:22 am
The most worrying news variants (South African, Brazilian, Kent) are emerging in locations with existing very high infection rates. Obviously it's way too soon to draw a conclusion from that but you have to accept it as a significant possibility.
The chance of any mutation will be the same per viral particle per time in any body, so I would accept that the vaccinated individual will have a lower chance of any particular mutation compared with an unvaccinated person, because they'll have a lower viral load.
Now, the evolutionary pressure will be for the virus to become easier to catch, easier to reproduce or easier to get out of the body.
Sure, an unvaccinated person might generate mutations that meet the above criteria, but there's absolutely no (selection) pressure to produce an escape mutation -- if it did achieve vaccine escape it would only be a fluke.
However, the evolutionary pressure for a virus in an vaccinated person is massively to create an escape mutation, even if that escape mutation is less virulent in the unvaccinated population. This is more likely to occur than a mutation that is both more virulent in the unvaccinated population and achieves vaccine escape.
For eg, consider a mutation that is 0.5 times as virulent in the unvaccinated population, but that is 2x more virulent in vaccinated bodies (than the original variant). The mutation might well be more likely to occur in the unvaccinated (because they've got more viral particles to mutate), but it isn't going to out-compete the original infection and will mostly 'die out' before leaving the body. However, that same mutation in a vaccinated person is going to out-compete the original virus, take over the infection and then try to spread itself to a new host.
This wouldn't be a problem if we vaccinated as few people as possible -- in this case there'd be lower chance of the mutation coming along (purely because of the number vaccinated being lower) and it would likely be rare in the unvaccinated majority (because it is less 'efficient' in that sub-population). Thus we would get an 'anti-herd-immunity' effect, where the unvaccinated would snuff out the escape mutations. By going for mass vaccinations we not only increase the numbers in which an escape mutation might occur, but also decrease the ability of the unvaccinated-herd to control the (less infectious in them) mutation.
All that said, what we have here is a complex situation where some decent modelling (along with existing data on the virus) could help identify the interplay between vaccine 'efficiency' (impact on viral load and transmission), mutation speed and proportion of the population vaccinated. This could then identify whether we should be vaccinating everyone or just the vulnerable. Unfortunately we don't seem to have had this done. Even worse, the populist message (coming from government scientists) appears to be based on an assumption that the vaccine is sterilising -- ie, vaccinate everyone as quickly as possible. My worry is that this lack of proper analysis is going to make things far worse.