Thread by @BillHanage

Have digested the latest excellent technical briefing from @PHE_uk on variants and Delta (the variant formerly known as B.1.617.2) in particular. as ever, all findings are context dependent and should be interpreted with care, but this is serious and deserves a wide audience 1/?

First, read all about it yourself (don't take my word for it!). Briefing here assets.publishing.service.gov.uk/government/upl… and Risk Assessment assets.publishing.service.gov.uk/government/upl… 2/?

This is from the risk assessment. Yes there is a lot of red. There is now very good evidence of increased transmissibility (will come back to that) compared with Alpha/B.1.1.7 (already quite transmissible). This is important. There is also... 3/?

Clear evidence of reduced vaccine effectiveness vs Delta. It is *not* clear how much of the apparent increase in transmission is due to this, and it is not clear what breakthrough cases look like right now. My own expectation is that they are milder than they would have been 4/n

(that's also a finding in this recently dropped preprint. I've not had time to fully assess it though, to figure out what it is based on so hoping someone else will!) medrxiv.org/content/10.110… 5/?

somewhat counterintuitively, more transmissible is MUCH worse than mild immune escape going forward, so unraveling this will be important especially for places with little current immunity and low vaccination 6/?

The data on vaccine effectiveness in the report is not broken down by vaccine unfortunately, but the assessment specifically states this. I can see several sources of bias and wouldn't call either way on this now. But nailing down the answer to this is going to be important 7/?

It is also possible that the reduced effectiveness might be consistent with much milder infection in vaccinees. But we don't know right now. Quite a lot of younger people in the UK, and indeed people in general in some places, are yet to receive any shot! 8/?

Next thing. Early data, but consistent between England and Scotland, suggests Delta is more likely to lead to hospitalization than Alpha. This is less secure than the other findings and as yet does not seem to have been broken down by vaccine status 9/?

This is going to take time to unfold and people should be patient. It takes time to resolve infections and see what happens in the course of disease, and the situation is changing quickly. We're not even 28 days from a lot of these diagnoses 10/?

(for those really paying attention, for the English data a stratified Cox proportional hazard regression was used that *did* adjust for vaccine status among many other things, but I think more work is still needed on this) 11/?

Reinfections don't seem to have been noticeable so far at least #OptimismSpa. This is good news, but the cohorts being followed for reinfection are far smaller than the total cohorts receiving vaccines, and so I am unsure how detectable a difference would be. Time will tell 12/?

This figure highlights schools as a common exposure in contact tracing. This should be interpreted in terms of local context I can't provide, but I believe that infection control in high schools in particular has been patchy and recently relaxed. Please read the next tweet 13/n

Note that before saying whether or not schools should be closed, you need to think about how you can mitigate transmission within them, and the consequences of transmission from kids to adults who may be vaccinated. Again, the nature of breakthrough disease matters a lot 14/?

👏🏼To all involved in producing this. The significance for the UK depends on how well the current vaccines protect (I'd guess quite well against severe illness) but elsewhere we need to be vaccinating more 15/?

I'd note too that I will revisit this as data comes in for the UK! The accelerated delivery of 2nd doses is certainly wise at the moment. let's not see how many times Delta can double before it runs out of people to infect 16/n

Finally this is awesome news, but there are *far* more than 80m people needing vaccines in the world. Once your community is highly vaccinated, please remember others that have not been as fortunate washingtontimes.com/news/2021/jun/… 17/end

Not least by specific vaccine received, controlling for age etc