Thread by @skepticalIDdoc

Lots of people are singing the Delta Blues these days. Let's discuss what we know about B.1.617.2 (Delta variant). Here's a 🧵

Here's a May summary of what we know courtesy of UK PH. Good certainty that it's more transmissible than original #SARSCoV2, and likely more than Alpha variant (B.1.1.7). However, uncertain about virulence (nastiness). Vaccine escape is conditional on one vs. two shots.

Here's a graphic of data on vaccine efficacy of one vs two shots against the Delta variant from a Preprint.

Another UK group examined neutralizing antibody titres (surrogate marker) in participants receiving 2 doses of vaccine and showed they were 5.8-fold reduced against Delta relative to wild-type #SARSCoV2 and similar to that observed against Beta (B.1.351). doi.org/10.1016/S0140-…

They went on to suggest that the benefits of delaying the second dose, in terms of wider population coverage and increased individual NAbTs after the 2nd dose, must now be weighed against decreased efficacy in the short-term.

So, just how prevalent is Delta variant in Canada? This is a tough question to answer as it's more difficult to test for. Screening for N501Y or E484K mutations doesn't help because Delta doesn't possess those mutations. We need to rely on whole genome sequencing; which is slow.

A rising % of cases in the UK, particularly in the NW are now Delta, but at the same time actual numbers are low, given the decreasing number of cases overall, but this sort of information does suggest a possible strategy.

That strategy would be to accelerate two dose vaccination in regions that have more cases attributable to the Delta variant. This would squash the emergence and have a spillover effect protecting other surrounding regions; a kind of "ring vaccination".
Stay tuned. <End 🧵>