Two strains of the coronavirus that were first detected in California have become “variants of concern” in the threat-ranking system used by the U.S. Centers for Disease Control and Prevention. The two variants—identified by scientists as B.1.427 and B.1.429—both appear to be 20 percent more transmissible than the original virus, and some COVID-19 treatments could be less effective against them. The good news, however, is that the CDC does not believe the approved vaccines are significantly less effective against the two variants, and no coronavirus variants are in the CDC’s highest threat level of “variant of high consequence.” Three other variants—one first detected in the United Kingdom, another in South Africa, and another in Japan and Brazil—are also on the CDC’s list of variants of concern. There are also three other “variants of interest.”