A few thoughts on current COVID situation in Europe… 1/
Any proposal to reduce COVID transmission that doesn’t now have vaccines and rapid tests front-and-centre is not a proposal that’s had much thought go into it. Booster data looks very good - roll-out of these is likely to play a large part in how well countries do over winter. 2/
I think any country reintroducing lockdown-type measures needs to outline very clear criteria for lifting them. What’s the exit strategy? When will these disruptive last-ditch measures finally be off the table? 3/
The various claims a few weeks ago suggesting country X in Europe had solved COVID and UK should copy them undermined the message that additional measures can be useful to reduce pressures over winter.... 4/
In particular, it gave ammo to nonsense reasoning like 'well country X has vaccination and testing and now has a large epidemic so these measures clearly have zero effect'. There are useful, efficient ways to reduce impact (see above) – need to communicate these clearly. 5/
The countries in the best position against COVID this winter aren’t necessary the ones that have had best outcomes against COVID to date. This is because epidemics become non-linear as immunity accumulates (i.e. more past infections can mean fewer future ones). 6/
This doesn’t mean past infections are good. It just means that if they’ve happened they will affect future dynamics. And linear thinking about what happens next for COVID (especially if rehashing pre-vaccine era talking points) will lead to increasingly inaccurate conclusions. 7/
Anyway, that’s it for now - dropping back offline for a while. 8/8
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A question I often see: if COVID transmission continues, when will it reach a stable ‘endemic’ state? One way to look at it: the dynamics of endemic infections are typically driven by emergence of new susceptibility. A few thoughts… 1/
Many endemic infections continue to circulate because new susceptibility is gradually accumulated as unexposed children are born: 2/
For other pathogens (like seasonal coronaviruses) new susceptibility can also come from waning of existing immunity, or antigenic evolution of the virus - which has the effect of making previously immune people susceptible to infection again: 3/
The terms ‘safe’ or 'unsafe' appear often in discussions of COVID threat, but they're vague, subjective words. What level of risk vs disruption is acceptable in long run (whether COVID or another disease)? 1/
As an example, I spent a chunk of my childhood paralysed and unable to walk thanks to a post-infection condition (GBS). Lingering effects for years. Not nice at all. But what should we as a society sacrifice to prevent a given level of risk? 2/
Vaccination is massively reducing COVID risk (at least in the countries that bought up most of the doses). So at what point are specific disruptive measures (whether at local or cross-border scale) no longer justified? 3/
In discussions of future COVID dynamics and potential for ‘herd immunity’, need to remember there are four main routes to immunity that can reduce Delta transmission - even though coverage often focuses on just one or two of them. A quick thread... 1/
Because Delta transmissibility is so high, and current vaccine less effective in reducing Delta transmission, vaccination alone unlikely to get R below 1. But that doesn’t mean immunity can’t drive R below 1 in future... 2/
There are four main routes to immunity to Delta:
A. Cross-protective immunity from vaccine designed against earlier variant
B. Cross-protective immunity from infection with earlier variant
C. Immunity from infection with Delta
D. Immunity from Delta-specific vaccine
3/
If - and it’s still a big if - exposure notifications from the NHS covid app/T&T were a major factor in driving the recent UK case decline, it’s worth considering what might happen next... 1/
It’s plausible that a rapidly growing epidemic + rapid testing availability + exposure notifications (both formal via T&T/app and informal among friends) has led to large numbers of people who would have been involved in transmission instead quarantining. 2/
If exposure risk is concentrated in time (e.g. because of Euro matches), quarantine timing would also have been concentrated in the period immediately after. Which means we can make a testable hypothesis about what might happen next… 3/