Sure, you're putting a human gene in there, but the subtle part of it is that when you have to recognize something as foreign, your cells chop up a protein and present IIRC 8-12 amino acids to present for immune cells (mhc-1). In that sense, the body is really sensitive to what proteins look like. I would imagine it not accepting a document that was .pdf instead of .docx. So when the protein is synthesized via recombinant means, I would expect some small change - if not even in terms of AA sequence (which Cuban scientists no doubt had to test for) then some glycosylation or other alterations that a bacteria would do.

The method isn't brand new or anything, I believe insulin can be made that way (not checking), it's just a marvel of science to me

iirc it's actually not that hard as an American? I think you have to state your purpose for visiting Cuba, and you check off the box that says "support of the Cuban people"? Might be other stuff but I think it's not actually that hard. There are also some leftist groups which take people down there

Go to a third country. Try to hitch a ride on a boat to Cuba. Hope they stamp a separate piece of paper instead of your passport so the tyrannical Biden regime doesn’t send you to jail

This is maybe last resort, but you can take a cruise ship there. As long as the boat is in the port, you don't need a passport to spend less than 24 hours in Cuba. It's how a lot of Americans do it.

But it would mean going on a cruise ship

Join a socialist delegation. Most good orgs will have a relationship with Cuba. You will usually be able to spend a week or so there as a group.

You'll be shuttled around but can get free time if you organize it.

These is at a higher dose but gives you a sense:

Although frequently effective, IFNα induces a variety of neuropsychiatric adverse effects, including an acute confusional state that develops rapidly after initiation of high-dose IFNα, a depressive syndrome that develops more slowly over weeks to months of treatment, and manic conditions most often characterised by extreme irritability and agitation, but also occasionally by euphoria. Acute IFNα-induced confusional states are typically characterised by disorientation, lethargy, somnolence, psychomotor removedation, difficulties with speaking and writing, parkinsonism and psychotic symptoms. Strategies for managing delirium should be employed, including treatment of contributing medical conditions, use of either typical or atypical antipsychotic agents and avoidance of medications likely to worsen mental status. Significant depressive symptoms occur in 21–58% of patients receiving IFNα, with symptoms typically manifesting over the first several months of treatment. The most replicated risk factor for developing depression is the presence of mood and anxiety symptoms prior to treatment.

A vaccine trains your immune system to respond, and interferon therapy is throwing the immune system into DEFCON 1

Useful and an achievement for Cuba but still worse than other social interventions

Cases would exhibit some seasonality instead of going to zero for years of new variants

This is not unique to Cuba of course

And of course, even China eventually succumbed to "letting it rip" instead of eradication which was, at one point, actually feasible.