I've seen most of Val Lewton's RKO horror movies, but there are still a few holdouts, and Isle of the Dead was one of them. It was an interesting movie to be watching right now, as it's about a group of people who have to quarantine on a Greek island because of a breakout of septicemic plague. But aside from a general recommendation to "not gather in groups," they don't actually do much to prevent the spread. I kept thinking, "Put a mask on! Don't talk so close to each other! WHY ARE YOU TWO MAKING OUT?!"
There's a reason it's not as well known or loved as other Lewton films like Cat People and I Walked With a Zombie - it's pretty slow. But it does have Boris Karloff, and a final act that includes some really cool and creepy imagery. Turns out there's a lot you can do in a black and white movie with a spooky woman in a flowing white dress.
Isle of the Dead is available to rent on most streaming platforms.