You might have thought the coronavirus vaccine race ended when Pfizer (NYSE:PFE) crossed the finish line first in December. But there's a new vaccine race underway. And that's the race to prove that a vaccine can protect against new viral strains. Variants from Brazil, the U.K., and South Africa worry the scientific community (and the rest of us) the most at the moment. But it's possible that new variants of concern will arise down the road.