The more chances you give the coronavirus to reproduce, the more mutations it will explore. Its proofreading system for reproduction is pretty good but not perfect, and that’s where the mutations come from. It’s a numbers game all the way. The virus is not thinking about how to evade vaccine-induced immunity; it’s throwing stuff randomly against every available wall in every available direction, and whatever sticks gets a chance to go on throwing some more. Remember, an unvaccinated person is still mounting an antibody defense against the virus – they’re just having to do it from scratch, rather than having a pre-primed leg up like someone who’s been vaccinated. The longer these infections go on inside human bodies, the more bets the virus gets to put down on the table. The good news is that so far, there is not much evidence that the virus is doing much evasion inside a given person during the course of normal infection.

So one key way to cut down on the odds of a nasty mutant popping up is to just keep the virus from reproducing so much. Cut down on the number of people it infects. When it does infect people, cut down on the amount of time it spends reproducing inside the body. These countermeasures are exactly what a mass vaccination program does. Fewer people get infected in the first place, and when they do get infected, their disease course tends in the great majority of cases to be shorter and milder. A nasty variant is almost certainly going to come up by accident, so let’s not have so many accidents going on constantly around the clock, around the world.