I like Ridley and what he writes is both interesting and makes sense. However, I think it is far from proven that airborne viruses universally get milder and others don't (so does he when you read the final paragraph). It isn't that I think he is wrong about Delta getting a boost from being spread in packed hospitals, whereas milder illness remain in home isolation. That is a selection factor for sure. However, random mutations are the source of new variants after which selection determines if they become the dominant variant (of which behaviour like hospital/no hospital is a part). Overall fitness will simply favour the variant that spreads/reproduces the best. Low lethality will favour a virus but if it kills slow enough the increased transmissibility might still give a greater fitness benefit. In other words a new variant could replace Omicron even if it was a bit more virulent and much more infectious, as there would be an overall selection pressure favouring the new variant. Of course a less virulent and more infectious variant could outcompete both but selection can only act of what there is to act upon.
I guess the next couple of years may tell us if the selection pressures of hospitalising the most sick (which of course we had to do) has slowed an inevitable decline in covid virulence. I'm not convinced but I hope I'm wrong.
Matt Ridley said:Yet here surely there is a worrying lesson about the past two years. In the weird world of lockdown, severe strains of Covid were favoured by selection. If you tested positive but felt fine you were told to stay at home. If you fell badly sick you went to hospital, where you gave your illness to healthcare workers and other patients. So mutants that were more infectious, such as alpha and delta, paid no penalty for being just as virulent, maybe more so. The natural evolution of Covid into just another mild cold was therefore possibly delayed by at least a year.
Of course, the idea that only respiratory viruses evolve to become milder is just a theory and needs to be challenged. The continuing virulence of direct-contact diseases such as measles and smallpox needs explaining, for example. But it is unforgivable for official advisers at Nervtag to be ignorant of the theory. Send for some Darwinians, Boris!
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