Epidemiologists battle changing strains of COVID virus...

Viruses mutate all the time, including the one, SARS-CoV-2, that’s caused the COVID-19 pandemic. Although most genetic changes are innocuous, some can make the mutant more adept at infecting cells, for example, or evading antibodies. Such “fitter” variants can outcompete other strains, so that they become the predominant source of infections. A succession of more-transmissible variants has…