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23 Jun, 4 tweets, 2 min read
If you're looking for a source for the surprisingly large number of cases reported in England today, I'd focus on school-age children. For example, this is the case series for 5-9 year-olds:
... and here are 10-14 year-olds:
there is continued growth in the 15-29 year old groups as well, but I'd say it's more in line with existing trends, rather than starting a new one.
looking for positives, one advantage of growth being in school-age children is that eventually, closure of bubbles / year-groups and even schools (see below) will kick in to control it. this isn't good but it's better than continued growth at that level.

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More from @JamesWard73

James Ward Profile picture
22 Jun
So here’s an interesting stat from the case data: over the last month, the case rates in England for men and women have been roughly the same. Which is unusual. (short thread, with thanks to @RufusSG for accidentally prompting me to look at this)
Over the last year, there has been a noticeable (c. 10%) bias towards higher case rates in women. Why is that? I’m not sure. Are women more sociable? More likely to work in key-worker roles? (health/care, retail etc.) Or just more likely to get a test when they are ill?
We can get a bit more insight by looking at the ratio by age group: it’s roughly the same in under-15s, biased towards women in working-age groups (15-65), towards men in the younger retired groups (65-85) and back to women in the elderly (85+). Image
Read 7 tweets
James Ward Profile picture
21 Jun
I’ve updated the model with all the latest data, and it’s mostly good news – at least for what happens over the next few months. There might be a bit of a ‘sting in the tail’ in the winter, but I think there are ways of dealing with that. Summary conclusions as follows: 1/
1. In my central case, the summer 2021 wave should be relatively small compared to previous waves (peaking around 5k hospitalisations per week)
2. Even in downside scenarios with higher R0 for Delta or a larger Step 4, there should be little risk of overwhelming the NHS 2/
3. However, opening earlier than 19th July would significantly increase those risks, and is not recommended
4. Assuming things go well in the summer (i.e. with a small wave), we may yet face the challenge of finding a few more % points of immunity in the autumn. 3/
Read 48 tweets
James Ward Profile picture
15 Jun
I think this deserves an explanation: why is it that countries that have already completed their epidemics with Alpha (or similar variants) might have an easier time with Delta than the UK, which was still in the process of opening up when Delta hit? 1/n
The answer has all to do with “overshoot”. For most epidemiological concepts there is an @AdamJKucharski thread to go with them, and overshoot is no exception, so I’ll leave you to explore here if you’d like a reminder of how this works: 2/n
Now for the purposes of this illustration, let’s assume we have two variants:
A, which has R0 of 4.0 and therefore -in a simple model- a herd immunity threshold (HIT) around 75%,
and B, which is 67% more transmissible than A, and so has R0 of 6.7, and HIT of ~85%. 3/n
Read 17 tweets
James Ward Profile picture
14 Jun
I know I’m meant to be reading the details of the SPI-M papers but there’s only so many coloured curves on a chart you can stare at before they all start blending into one. I’ll re-convene on that tomorrow, but in the meantime I found something interesting in the case data. 1/7
This is plotting the growth rates for the 5-year age groups up to 30 over the last 3 weeks. You can see the explosive growth in the 20-24s and 25-29s following Step 3, and then a significant deceleration (falling growth rates) over the last few days. 2/7
On the other hand, the growth rate in school-aged children (5-9 and 10-14) looks to be resurging, having taken a short break over half term – suggesting that we might have a rocky few weeks ahead in the last few weeks of the school summer term. 3/7
Read 8 tweets
James Ward Profile picture
14 Jun
I promised that I would come off the fence re. plans for Step 4 by today, and I’ve left it right to the last minute, but now I will: I believe we should be delaying by 4-6 weeks. And if asked to pick a specific date, I’d go with 26 July (5 weeks on from 21 June). 1/n
(this has the marginal presentational benefit of using the government’s standard step length, so Boris can ask us all to take “one more step” on the journey back to normality). 2/n
This would normally be the point for me to launch into a long thread on the reasons why this is the best approach, and all the alternatives are sub-optimal. But I actually need to do some work today, so I’m not going to do that (if I get a chance I’ll add something later). 3/n
Read 7 tweets
James Ward Profile picture
11 Jun
@kallmemeg has kindly nominated me to undertake some vaccine efficacy (VE) estimates from the data in Table 6 of the latest PHE Tech Briefing. I know the number of deaths in the “double vaxxed” column has been causing concern, but I think it’s OK. 1/n
My overall conclusions are:
1)The vaccine’s efficacy vs. disease is hard to deduce from this table, as it’s sensitive to the exposure risk assumption, but a rough estimate is consistent with the PHE’s figures in Table 18 (i.e. 33% after 1 dose and 80% after 2 doses) 2/n
2)The VE vs. hospitalisation and death appears robust to different assumptions of exposure risk, and implies that the vaccines are maintaining good protection (~80%) after 1 dose, and very strong protection {>95%) after 2 doses. 3/n
Read 22 tweets

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