Thread by @ewanbirney

Sitting in softly air conditioned room on the Genome Campus, Cambridgeshire hot and sunny outside, musing about Corona this week. TL;DR - the UK looks like it is sensibly going to delay; the Delta variant is more transmissible and this implies at least one more wave worldwide.

Context: I am an expert in genetics and computational biology; I know experts in viral genomics, infectious epidemiology, clinical trials and immunology. I have COIs - I am a longstanding consultant to Oxford Nanopore and I was on the Ox/Az trial

Reminder: SARS-CoV-2 is high infectious virus which causes a severe disease, COVID, in a subset of people, often leading to death. No healthcare system in the world could cope with unfettered transmission of the virus, so a variety of control measures have been performed

The most successful measure is vaccination, which both dramatically reduces the incidence of severe disease (and hence death) and also reasonably significantly reduces the transmission of the virus.

The virus has continued to evolve over the last 18 months. The dominant strain in the UK, Delta, (B.1.617.2, first identified in India) is both *more* transmissible than the previously evolved Alpha strain (B.1.1.7) and, frustratingly, takes less notice of a single vaccine dose

This changes the calculus of how fast transmission will happen in the UK relative to vaccination rates, and because of this the UK Government looks likely to delay the final stage of reopening. This is ... sensible with far lower risks, and has paths ratcheting open.

It's worth stressing that *whenever* a country opens up fully (eg, Israel with B.1.1.7) there will be an "exit wave" and indeed one of the complications in the UK has been how much Delta vs how much stage 3 transmission change has occured over the last 4 weeks.

A problem in communication here is going to be that there is going to be a number of people going to hospital over the summer with COVID in the UK, in any plan. What want is this to be within the bounds of the UK healthcare service (NHS).

I am less concerned though by the UK; the vaccination strategy works, the ability to see and quantify a new dangerous variant has happened, and an appropriate response looks in the works.

More complex is how Delta travels through the world. It has already ravaged India, with large recorded deaths and probably far higher unrecorded (I am not an expert on COVID in India, so this is what I get from colleagues and Twitter).

The differential transmission impact of 1st doses from Alpha to Delta is also going to be headache; countries that can easily control transmission of Alpha partly due to vaccination might find it far far harder to control Delta; Canada is particular at risk here.

For Europe, it will be important to get to School holidays so that there is less mixing and more outdoor activity over the holidays before Delta rises (indeed, this much the strategy in the UK with the delay of 4 weeks).

Balancing when to have that final exit wave is going to be interesting and beyond the obvious - vaccinate as fast as possible - I think some care needs to taken on September/October, and the number of unvaccinated at risk people in each country then will be key.

Most of the non-developed world has a longer horizon, and we should, sadly, expect yet another evolution of the virus at some point in some place. This virus is not going to magically go away; our best solution is managed endemic virus with regular boosters for people at risk

The support for vaccine roll out by @gavi, G7 pledges (though details, details, details - how much actual vaccines, when being the most important) is great, but there is a still a long road worldwide.

A reminder that this is a humanity vs virus fight; all humans need to work together, and the real population unit to consider, slightly awesomely, is everyone on the planet. We've got a long way to go, but we do have the tools to get there.