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12 Apr, 8 tweets, 2 min read
At the end of last week it was reported by the Telegraph that we would achieve herd immunity today (Monday 12/04/21).
There are a number of reasons I don't believe this to be a helpful headline.
Perhaps most importantly, telling people we have reached herd immunity will give people the impression that it is safe to open up completely and infections will still decline.
It's not hard to imagine that this may have a detrimental effect on behaviour and compliance.
Talking about herd immunity as "all or nothing" is not particularly helpful either.
Generally as immunity builds up in the population it slows the spread.
Even when spread starts to decline, if R stays close to one then lots of people may still get infected as cases come down.
Herd immunity is not a threshold we need to reach and stop to congratulate ourselves, but a barrier we need to smash through and keep on going. The more people are vaccinated the safer we become
Whether we can reach a level of immunity at which transmission eventually stops when we relax all restrictions remains to be seen.
More of my thoughts on herd immunity and herd immunity thresholds here:
The telegraph headline is based on modelling by Professor Karl Friston at UCL, who is a member of the independent SAGE group for whom I also volunteer.
This does not mean I endorse his modelling.
Indeed, as I have said above, in this instance I disagree with its main message.
At least since I joined independent SAGE in October the group have not relied on/used this dynamic causal modelling modelling framework.
Certainly none of my opinions or public communication have been formed/guided with reference to the results of these models.
Professor Friston has now clarified his position on his DCM website.
fil.ion.ucl.ac.uk/spm/covid-19/

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More from @Kit_Yates_Maths

Kit Yates Profile picture
12 Apr
A short thread on herd immunity.

Herd immunity is an incredibly important concept. It suggests diseases can be eliminated without everyone having immunity.

If you want to eliminate an established disease then herd immunity is the way to do it.

1/10
It's important to note that people can gain immunity in two different ways. Through being infected and recovering with immunity or through being vaccinated.

Hard to believe it needs to be said but, the best way for people to get immunity is through vaccination.

2/10
When enough people have immunity for the reproduction number to go below one the disease will start to decline.

This level of immunity is often called the herd immunity threshold or the critical immunisation threshold.

3/10
Read 10 tweets
Kit Yates Profile picture
2 Apr
Despite the good news in cases over all (see thread below), looking at the data unsegregated by age masks what is happening for different age groups.

We are almost seeing two different epidemic trajectories by age across the UK.

A short🧵
Case rates for ages 20-59 and over 60s remain stable or have reduced slights in most regions.
But case per 100K per week for the under 20s have risen week on week in most regions (with the exception of the North East).
Read 8 tweets
Kit Yates Profile picture
2 Apr
No @IndependentSage briefing today, but I don't want anyone to go into withdrawal though lack of data so here's a short thread on cases and positivity rates.

Overall it's good news.
Positivity rates low and falling or flat across all nations and most of local authorities.
Cases per 100K per week have plateaued for Scotland, England and Northern Ireland with slight falls in Wales.
This is good news, especially after some slight rises previously.
Positivity rates look even more encouraging.

All nations are well below the 5% threshold and continuing to decrease week on week.
Read 10 tweets
Kit Yates Profile picture
26 Mar
A quick look at the situation of some of our mainland European neighbours.
Summary: There is a third wave happening in Europe at the moment, but it is not the same in every country.
There is no reason to believe that this wave will "Wash up on our shores".
Cases are rising in many European countries as the impact of the higher transmissibility of the UK variant B117 kicks in.
Not all nations are experiencing this wave though. Spain for example has relatively low levels of cases.
The UK still far outranks any other European country in terms of total death toll, although the UK's trajectory is much flatter and other nations like France and Germany are seeing significant rises.
All countries are in a race to vaccinate their populations...
Read 8 tweets
Kit Yates Profile picture
26 Mar
A thread on vaccination data.
Summary: Rollout is going well still although we anticipate a slow down in April due to supply.
Second doses need to keep pace with first doses.

There are stark disparities in those who plan to take up the vaccine based on deprivation and ethnicity.
Vaccination continues apace. Despite record numbers at the end of last week, this week has seen a bit of a slow-down.
More second doses are being given to keep pace with the rate of increase in first doses 12 weeks ago.
We will see first doses drop off in April due to supply.
Over 53% of the adult population have received their first dose now and around 5% have received their second dose as well.
Read 10 tweets
Kit Yates Profile picture
26 Mar
A short good news thread on critical care capacity/occupancy (England).
Summary: Adult critical care bed occupancy is coming down allowing hospitals to start to return to normal functioning.
Adult critical care bed occupancy has fallen in most English regions and is now down below the suggested 80% of capacity threshold in all regions.
(Orange dots are this week's occupancy grey dots are last week's).
Nationally, this year's adult critical care occupancy (blue dashed) has fallen close to last year's levels (orange dashed line) and surge capacity (clue full line) is being decreased correspondingly.
Read 4 tweets

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