First of all, nobody knows if Steve Harris is unvaccinated. It’s a fairly large leap even if the British Lion cancellations don’t paint a great picture of the band’s approach to COVID. Being against anti-COVID measures, as stupid as a stance as it is, doesn’t equate to being anti-vax. There are a lot of prominent musicians (Eric Clapton for one) who have been pretty vocal about being anti-vax or whatever else, but are still vaccinated.
IMO Iron Maiden is a too-big-to-fail organization. Steve could be anti-vax but when push comes to shove he’s probably going to be pressured by the Maiden management to get vaccinated anyway (I imagine this is possibly what happened with Clapton). Unlike others on here I’m not going to pretend to be an expert, but I would assume Maiden (as a business with many employees) stands to lose a ton of money if they can’t tour anymore. And even if they were to tour, having an unvaccinated person in the band would be a major liability. I doubt even Steve has enough weight to bring the whole thing down because of anti-vax stupidity.
But again, we don’t even know what happened with the British Lion tour, so it seems silly to jump to Steve being anti-vax.
Something else to consider, Maiden has announced new dates in 2022 that aren’t just rescheduled from 2020. If Steve’s vaccination status was in question, I’m not sure if Maiden would be announcing shows with their ability to tour being in doubt.