Alpha, Delta and More: Why Virus Variants Are Causing Alarm

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 emerged over the past year, each harboring a constellation of mutations. The most worrisome so far is the so-called delta variant. It’s become dominant in much of the world since its discovery in India in October 2020, leading to surges in cases and hospitalizations, especially in places where less than half the adult population has been fully immunized.

During replication, a virus often undergoes genetic changes that may create what are called variants. Some mutations weaken the virus; others may yield an advantage that enables it to proliferate. If changes produce a version with distinctly different physical characteristics, the variant may be co-termed a strain. A variant that deviates significantly from its viral ancestors may be identified as a new lineage, or branch on the evolutionary tree. In general discourse, however, the terms are often used interchangeably.