The CDC described Delta as more transmissible than the common cold and influenza, as well as the viruses that cause Ebola, smallpox, MERS, and SARS, Ebola—and called it as contagious as chickenpox in an internal document, a copy of which was obtained by and reported on in The New York Times.
Delta is the name for the B.1.617.2. variant, a SARS-CoV-2 mutation that originally surfaced in India. The first Delta case was identified in December 2020, and the strain spread rapidly, soon becoming the dominant strain of the virus in both India and then Great Britain.
Delta VOC in Scotland was found mainly in younger, more affluent groups. Risk of COVID-19 hospital admission was approximately doubled in those with the Delta VOC when compared to the Alpha VOC, with risk of admission particularly increased in those with five or more relevant comorbidities. Both the Oxford–AstraZeneca and Pfizer–BioNTech COVID-19 vaccines were effective in reducing the risk of SARS-CoV-2 infection and COVID-19 hospitalisation in people with the Delta VOC, but these effects on infection appeared to be diminished when compared to those with the Alpha VOC.