Alejandro, that's a pretty common issue to face: how do you take a set of facts and turn it into a story for a documentary film? And I think there's plenty of people who end up making films that probably should have written a book or an article instead, because that would be a more efficient way to present the facts.
It does sound like you've got a great subject, full of cinematic potential. But I think you're right to be trying to figure out what your story is, because that's really the key. As you obviously know, having characters with story arcs and plot points is a great way to structure a film. I would advise you not to give up on exploring characters, even if you can't be there to shoot over a long period of time. You can get a lot out of following people for a day, observing them in different settings, maybe interviewing them briefly, even getting interviews in different settings. Having people in your film to personify the issues you're documenting will make your film come more alive.
As an example, I worked on a film "Wonder Women" for which the filmmakers did a great job at presenting facts and an argument, mostly through talking head interviews. But they also found characters who could illuminate aspects of the argument, and there were little 5-minute segments on these characters. So you don't get a feature-length story development, but you still get a lot.
Another way to consider the problem of finding a story: you can use history as the story of the film. So in your film, we might have a brief intro to the Cuban medical program today. Then we go back in time to its founding, see archival, find out how it began, see how it developed, etc. Even if you keep going back to the contemporary footage and we see what's happening today, you can still use the history-telling as a structural device. So we keep going back to the history and seeing how the program developed and became what it is today.
That's more or less the structure of "Wonder Women." There's a lot of exploring the contemporary world, but the whole thing is structured around a history (of women and popular culture) of the 20th century. So that you get to the end, and it's a natural place to ask questions about what's going to happen next. Which can work as an ending to your story, even though it's not final.
Another way to have a story is to have some person exploring the facts/issues and the story becomes their story of learning. That's the approach of a film like Sicko, where Michael Moore is the character who pretends to learn about the topic. Of course, Moore is actually constructing a sophisticated and effective argument. But there is a sort of story there, with himself as the character who grows and changes.
Maybe you don't want to insert yourself into the film like a Michael Moore. But you can get somebody else to be on-screen, like one of the students, or a journalist or an academic, or a doctor interested in this subject. And the film follows their story of coming to understand the issue.