Synopsis The P681R mutation, which is said to drive syncytium formation - fusing of infected lung cells - associated with severe forms of SARS-COV-2, or Covid-19. AP The study paper finds that the P681R caused formation of larger syncytia (fusion of infected cells in lungs) than other variants and effected higher pathogenicity even at a lower viral load. Two separate studies in India and Japan on the Delta variant point to a key mutation and a possible combination with another as important factors behind its fitness advantage and ability to cause severe disease. Though early studies had already indicated that the Delta variant is able to significantly escape vaccination-induced immune response and transmit faster than most known Variants of Concern (VoC), there was not much clarity about its virological properties. The new studies have attempted to answer that question and the answers appear to lie between mutations P681R and T478K, as per assessments so far. Three distinct subtypes of the B.1.617 have been identified so far -- the B.1.617.1, the B.1.617.2 or Delta, and the B.1.617.3.