A new variant of the coronavirus has developed in India, one that is making public health officials worried because it may be causing the country’s terrible outbreak and could reduce the efficacy of available vaccines.

The India variant, known as B.1.617 and first identified in October, has been dubbed the “double mutant” variant because it contains two mutations of interest, E484Q and L452R. These are mutations on the spike protein, the part of the virus that attaches to a cell.