I do not credit their motives as being altruistic.
Absolutely correct.
I mean, I'm sure some of them are, having been sucked in themselves.
But just to put it in perspective, we know that anti-vaxxing was one of the topics Russian troll-farms chose to amplify long before the Covid came along. It just didn't hit the headlines then the way it does now.
I don't know whether the Russians picked it as merely a random divisive topic (they go for pre-existing divisive topics as easy meat), or whether it was more strategic and they saw anti-vaxxing coming in handy some day. The knowledge that there'd be a pandemic reaching the rich English-speaking world eventually was hardly secret: the Obama White House even prepared a task force in case it happened on Obama's watch.
That's just the Russian behaviour. Like all major events, there are opportunists of all sorts happy to swoop and make the most of it – for as little reward as the joy of having their 15 mins of fame.