Update (May 11): CNBC reports that the World Health Organization now considers B.1.617 a variant of concern, following an analysis by one of its working groups that indicated the variant is more transmissible than the original one.

With India in the grip of a devastating second wave of COVID-19—the country recorded more than 368,000 new cases and 3,417 deaths from the disease yesterday—some have suggested that a variant first detected there in October could share some of the blame. The B.1.617 version of the coronavirus carries the ominous nickname “double mutant,” but it has more than two sequence changes from older SARS-CoV-2 variants, and little is known so far about the effects of these alterations, if any, on disease severity or the virus’s ability to evade immunity gained through infection or vaccines.

One preliminary bit of insight emerged on April 23, when researchers reported in...

B.1.617’s double mutant moniker comes from changes it harbors that are similar to those in other known variants. One mutation, known as L452R, is also found in the B.1.427/B.1.429 variant first identified in California, where it has been associated with increased transmissibility. Another B.1.617 mutation, called E484Q, is similar to the E484K mutation found in the P.1 variant that was first detected in Brazil and the B.1.351 variant, also known as the South African variant. E484K is known as an “escape mutation” because it appears to help the virus partially evade immunity conferred by prior infection or vaccines, according to The BMJ.  

See “Side-by-Side Comparisons of Important SARS-CoV-2 Variants

B.1.617 is now the dominant variant in India’s hardest-hit state, Maharashtra, according to Nature. In its most recent epidemiological update, released April 27, the World Health Organization (WHO) notes that multiple other variants are also circulating in the country, and that “Preliminary modelling by WHO based on sequences submitted to GISAID suggest that B.1.617 has a higher growth rate than other circulating variants in India, suggesting potential increased transmissibility.” It has also been found in at least 16 other countries, the organization notes. WHO still lists B.1.617 as a “variant of interest” rather than a “variant of concern,” because its effects on epidemiology or vaccine effectiveness, if any, are uncertain.

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