One argument put forward for July 19th UK reopening is to bring infections forward to reduce winter wave. To be honest, I’ve always found idea that we could tailor a pandemic to get 'better' sized future waves a bit absurd - whether in spring 2020 or now. A few thoughts... 1/
For me, main issue now is medium term disruption vs medium term epidemic size. Many people now seem OK with R>1 in countries with relatively high vaccination % (at least implicitly, given they aren’t advocating for the strong measures required to guarantee R<1). 2/
Given R>1, much of Europe faces large epidemics likely to end with accumulation of immunity in next few months - much of it from infections. Reopening would accelerate this, but won't be difference between epidemic & no epidemic (unlike, say, reintroducing measures to get R<1) 3/
That doesn’t mean we should be fatalistic and say ‘well if R>1 anyway it doesn’t matter how big’. Having R=1.4 rather than R=2 in short term (as hypothetical e.g.) would allow more people to be vaccinated before they get exposed. But still need to think through tradeoffs… 4/
As a *very rough* illustrative example, if R=1.4 currently, a simple model would predict epidemic resulting in around 50% of remaining susceptible population being infected (here 'susceptible' includes any breakthrough infections in vaccinated groups). 5/
If R=2, then this *very rough* example has around 80% of remaining susceptible population being infected. Detailed models would give more robust estimates, but punchlines are: i) both scenarios mean large numbers infected ii) epidemic smaller in scenario where R kept lower. 6/
But, of course, keeping R lower requires ongoing measures. Some wouldn't be so disruptive, e.g. masks on public transport, rapid tests to check infection status. But some more disruptive, e.g. keeping venue capacities constrained, quarantining large numbers of contacts. 7/
Some measures, such as testing symptomatic cases, also provide important situational awareness about epidemic and variants - which is particularly crucial if we want to track new variants spreading among vaccinated individuals. 8/
Everyone will have different preferences about what medium term measures are appropriate to prevent a given number of medium term cases. To some extent, it's also possible to work out 'revealed preferences' by comparing what people are and aren't arguing for. 9/
How countries approach next steps will depend on where they are with cases, vaccine roll out etc, but worth reading up on international situation to get idea of how tradeoffs viewed elsewhere, e.g. Singapore:… & Australia:… 10/10

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More from @AdamJKucharski

11 Jul
In discussions of Delta in UK & much of Europe, it's worth remembering that to avoid a large number of future COVID-19 cases at this point, countries would need to dramatically curtail social mixing - otherwise they've still got a rising epidemic, just with a flatter peak. 1/
Look at recent action in Singapore, for example, which has now fully vaccinated 40% of population. Article from May:… and last week:… 2/
Big difference with UK, of course, is case numbers. Given current case level in UK, if test & trace was suddenly omniscient with full adherence, millions of people would now be in quarantine. In terms of disruptions, it would be somewhat equivalent to a snap ban on gatherings. 3/
Read 6 tweets
4 Jul
I've always found it very unhelpful that 'self-isolation' is used to refer to both isolation and quarantine, but the distinction is now becoming increasingly important... 1/
To recap, isolation is for people who are confirmed to be infected; quarantine is for people who currently seem healthy but may be infected. A stay-at-home order is basically a large, untargeted quarantine (some countries even call it 'community quarantine'). 2/
As vaccines reduce infections/transmission, countries are re-evaluating approaches to disruptive quarantine, whether for travellers or contacts of cases (e.g. in US:…). However, we need to be careful about jumbling isolation and quarantine together... 3/
Read 5 tweets
2 Jul
Schools, workplaces, pings from COVID app… Having high UK case numbers over summer will have huge implications for quarantine burden. A few thoughts… 1/…
Because vaccines reduce onwards transmission, contacts are becoming less risky on average - which means that for a given value of R, each case will typically have far more contacts than they would have had last year. 2/
Under pre-pandemic contact patterns, a typical case will have 25+ contacts while infectious (…). That’s a lot of people who could potentially be quarantined per case. 3/
Read 4 tweets
18 Jun
Any discussion of daily testing vs quarantine for contacts of cases in schools needs to address the key epidemiological question: if a child in a school tests positive, what do you do next? 1/
Encouraging ventilation etc. to reduce transmission risk is important, but you still have to decide what to do about a positive result. Do you quarantine their contacts or not? 2/
If you decide to abandon quarantine because you think ventilation etc. has sufficiently reduced risk, then this still means accepting higher transmission risk than if quarantine had remained in place. 3/
Read 8 tweets
11 Jun
How long could UK cases continue to rise? And how might hospitalisations increase alongside? A thread... 1/
Despite relatively high vaccination rates compared to other countries, cases are growing and in many areas R is now above 1.5. Remember, immunity is already 'priced in' to this number - without vaccination and the social distancing still in place, R would be *much* higher. 2/
If R is 1.5 and contacts/control remain the same, then we'd need remaining part of the population who could potentially spread COVID to shrink by at least 33% before R drops below 1 & epidemic peaks. This would require additional immunity, either from infections or vaccines. 3/
Read 9 tweets
5 Jun
A common Q: “how can COVID hospitalisations in UK still grow if vaccine % high?” Answer: look at the data. Average was ~120 daily COVID admissions over past week. These would have been infected about 2-3 weeks earlier, when case numbers ~2000 per day. This shows two things... 1/
First, there was still a group at risk of hospitalisation a few weeks ago. And second, this risk was large enough to show up as hundred of admissions in recent data, even though cases were at relatively low levels. 2/
So the key question here: if case numbers were to grow X times larger, why wouldn’t hospitalisations also grow X times larger? 3/
Read 4 tweets

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