Two years into the coronavirus pandemic, Americans can be forgiven if they’ve lost track of the latest variants circulating nationally and around the world. We’ve heard of the alpha, beta, gamma, delta, and omicron variants, but a new Greek-letter variant hasn’t come onto the scene in almost half a year. Instead, a seemingly endless stream of “subvariants” of omicron, the most recent Greek-letter variant, has emerged in the past few months. How different are these subvariants from one another? Can infection by one subvariant protect someone from infection by another subvariant? And how well ar...