— Here’s the latest on transmissibility, virulence, vaccine efficacy, and more

by Kristina Fiore, MedPage Today 

With reports about the more transmissible Delta variant, and now “Delta plus,” taking the media by storm, here are the essential facts when it comes to the latest variant in the spotlight.

What Is the Delta Variant?

The Delta variant, or B.1.617.2, first emerged in India, with the earliest samples dating to October 2020. However, it didn’t raise alarms until India faced down a major COVID-19 surge this spring, when it became a variant of concern, according to both the CDC and the World Health Organization (WHO).

B.1.617.2 is a variant of the first “India” variant, B.1.617 (named Kappa and only a variant of interest). There’s also B.1.617.3 (variant of interest) and more recently, B.1.617.2.1, which has been called “Delta plus” in the media and doesn’t yet have a spot on the CDC or WHO lists.

The chief concerning mutation in Delta is L452R, which changes the spike protein. “Delta plus” appears to have acquired the K417N mutation, which also changes the spike protein. Both variants also have several other mutations in spike, as well as other genetic changes that appear to have less of an impact.

Is Delta More Transmissible?

Delta does indeed appear to be more transmissible. The CDC cites a Public Health England study of 3,765 cases (household clusters), matched with 7,530 controls (single case in a household), to estimate the odds of household transmission of Delta compared with the Alpha variant (B.1.1.7), which first emerged in the U.K. This study found that Delta was 64% more transmissible than Alpha when it came to household transmission (95% CI 1.26-2.13, P<0.001).

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