If you look at data from the Kings/Zoe symptom tracker in the Spring and the Welsh and English lockdowns in the autumn there are clear trends that show the impact of a lockdown within specimen data 6-8 days after the measure comes into force.
This is due to what has been called baked in infection, people who caught the virus just before lockdown and who then tested positive after lockdown along with people they have passed the virus to. This seems to maximise at 6-8 days then declines. So what can we make of the current specimen data profile which seems to show the peak as the 17th December 2 days before the official lockdown was introduced.
Before I go further a little on the science. Early in the outbreak Pueyo (2020a) produced an article "the Hammer and the Dance" this postulated the need to hit the virus hard to suppress numbers than enter "the dance" where restrictions would be used with multiple lockdowns to keep virus levels low until a vaccine arrived. This is essentially the model the UK government has pursued. Since the paper was published the "Covid Zero" approach of China, Taiwan and New Zealand has been recognised as the better solution for health and economic outcomes. Despite attempts in Wales to follow this reaching as low as 6 cases on day in the summer the reseeding from the UK decision to allow European travel and the emergence of the Kent strain means at least for now Covid is endemic in the UK.
The importance of the dance is that it calls for various measures to restrict social interaction right up to a full lockdown with curfew. This is achieved by adding together lots of incremental steps that combine to reduce the level of R to below 1.
So back to Wales the peak was not triggered by the official lockdown but could there have been a natural one? Remember R has to drop below 1 and a lockdown takes 7 days to show up in the data. For smaller individual impacts the return is likely to be smaller and hence take longer to show up. So lets step back 7 days to the 10th and look at what had happened around that time window.
4th Dec Hospitality ban enters effect / Student travel window commences
11th Dec Last day of term for Secondary schools
If we look at students first with many living in communal halls or HMOs the risk of contact with the virus is likely to be higher than a typical household due to increased interaction. The age group had also been identified as a driver of the autumn surge not for behavioural reasons but due to the dense accommodation patterns. Moving this group back into standard households will have had an impact on R.
Hospitality as a sector have done everything possible to make themselves covid secure however the increased transmissibility of the new strain will be testing those precautions to the limit. Outside of the household hospitality also provides the longest interactions in enclosed spaces after home and some workspaces. Prior to the main peak there is a small shift in the rate of increase on the 14th, 10 days after hospitality restrictions were introduced. This suggests they made a contribution but that on their own they wouldn't be enough to keep this new strain under control.
Before I look a schools its worth looking at behaviour change. Since the start of the pandemic Google have been publishing data on movement trends at COVID-19 Community Mobility Reports (google.com). If you look at the relevant window you can see that there is a general drop in attendance at recreational sites across Welsh Councils. This is a response to the measures above and indicative that there will be some impact.
This leaves schools. Contrary to popular belief schools are not a major driver in the early autumn wave. Data published by the Welsh government and data I have been briefed on in Powys shows that the majority of pupil infections came from outside contacts that were then identified within a school or the school was notified leading to isolation. A number of staff outbreaks have been identified. So with the original variant schools staying open was a viable proposition. What is unclear is if this is still true of the new variant. In Kent and London the virus was able to gain a foothold under English lockdown rules where schools remained open. In Wales however the incidence of the virus has reduced before official lockdown but after the end of term where the impact on R of schools not being open was in play.
Frustratingly the PHW latest bi weekly report sheds only limited light on the situation The latest sample date of the 12th means we were still in a rising phase and the age cohorts fail to separate out 16-18 yr olds from younger secondary pupils. This means there are still questions for those with access to more detailed info to answer.
Is there an increase in pupil infections between the pre and post firebreak period?
Has the pre firebreak profile of single or unlinked school cases been maintained or are we now seeing in class infection?
Is there an change in the infection rates amongst adults with primary age pupils a possible indicator of dropping off infections?
Is there evidence of Teacher/pupil infection?
Are infection rates within schools higher or lower than the local community incidence?
Throughout this pandemic the data hasn't lied. Changes to social contact had mirrored in infection rates. Reduce theoretical R you see a response in the data. It is clear to me that the combination of reduced hospitality and recreation activity, students returning home and the end of the school term plus some behavioural change have resulted in at least for now a significant impact on the levels of infection by creating a "natural lockdown".
Based on publicly available data it would suggest that the absence of pupils from school was the final tipping point between expansion and contraction of the pandemic in the current environment. What is needed now is some significant research using PHW and TTP data to ascertain what it is exactly about schools that gives such a significant boost to reducing R before we can determine how best to open them in the new year.
References Pueyo (2020) Coronavirus: The Hammer and the Dance | by Tomas Pueyo | Medium
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