From the Wikipedia page, it seems like a fairly normal cancer vaccine. The thing limiting these in North America and Europe is that you can’t legally do drug trials on people until you’ve tried all the approved medicines for that condition first, as trial drugs might do nothing and might cause side effects, and the placebo control group would literally not be getting any treatment. By the time cancer patients have tried all the existing treatments, they’re usually either already dead, or already cancer-free, so the only trial participants left are already nearly dead, and likely to keel over immediately no matter how good the trial drug. That means things that drug companies have known will work for over a decade still aren’t available, and once they are, they’ll need to be unreasonably expensive just to break even.

Either this one has finally got over these kinds of hurdle after years of effort, or Cuba’s been doing trials that wouldn’t be legal elsewhere. Even if they have, it’s not necessarily a criticism - if a trade embargo stops you accessing lots of medicines, then you need to get through fewer of them before you’ve tried everything available and can start trial drugs. Once it’s fully approved, it won’t need to be expensive, as the research costs can be offset against the cost savings from treating patients, as everything’s state-funded.