Dr. Fauci is worrying about variants of the virus that could emerge that are even worse than Delta. Future variants where even the vaccines, we now have, could be less effective. The vaccines are working good, now at least.
Some folks blame the risk of these new variants on vaccine reluctance in this country, but I think the problem is deeper than that. Chances are one of these variants would, most likely, arise in some other part of the world where the vaccine is less available.
Basically, I think people, who are reluctant to get the vaccine, are shooting themselves in the foot since the vaccine is working well for now. The best argument for the vaccine is self interest for protecting one's self.
As for future variants that could arise, the bigger problem is still lack of vaccine availability worldwide. Chances are, a bad variant could arise in the US, but more likely, it would arise somewhere among the nearly 8 billion people worldwide. In some of those places, the problem of lack of vaccine supply is still larger than vaccine reluctance.
Vaccine reluctance moves to first place as a problem after supply becomes plentiful.
Worldwide distribution of vaccines is happening at a fast pace, but it still takes time to roll anything out to billions of people.
Some conservatives, in USA, are now using this worldwide threat as an excuse to complain about immigration. I see immigration as only one small part of the bigger picture.
I heard someone, on a radio talk show, suggest that people arriving in US either legally, or illegally should be required to get vaccinated. Folks in US custody at the border could be required to be vaccinated unless there is a medical reason against it. If they refuse, deportation becomes more likely.
Travel is a factor, but in our modern world, we can't totally seal borders, stop air travel and so forth. Not without severe harm to our modern economy and ways of life. I hear that Canada will require proof of vaccination at the border when it reopens.
Bad variants of the virus may cause us to have to shut down parts of the economy again. There would be booster shots and tweaks of the vaccines to deal with that, but these remedies take time; probably not as long as development of the original vaccines, but still time.
I figure, "get vaccinated and enjoy life while you can," but who knows, for sure, what the future may bring. Trust that most of the scientists are trying to do the best they can given this changing situation.