The US Centers for Disease Control and Prevention said this week it had designated a coronavirus variant first seen in India as a "variant of interest," adding it to the growing collection of viral variants it's keeping an eye on. Vaccine makers are so worried about the chance new variants will escape the protection offered by immunization that they are already testing booster shots and tweaking their vaccine formulas to specifically target some of the more troubling variants. And doctors around the world are warning that even more variants will arise as the virus continues to evolve inside the bodies of the tens of millions of people it is infecting.