Read on Twitter
1/ Stunning insights from the NHS symptom-reporting app. It shows a dramatic decrease in live symptomatic cases, starting on 1st April, just 8 days after the UK lockdown began.
2/ The % decrease is vastly greater than the slight decrease in hospital admissions over the same period.
Why? Here's my proposed explanation: (THREAD)
Why? Here's my proposed explanation: (THREAD)
3/ There are two key facets to this. First, a delay effect. Hospital admission comes maybe 1-2 weeks after symptoms appear. Thus the admissions curve probably peaks a week later than the symptomatic curve, just from this effect.
4/ More importantly, there is a demographic effect. Prior to lockdown COVID-19 was rampant among the working-age, socially active, young end of the population distribution who are resilient to the disease except in rare cases.
5/ Older people during that period were cushioned from the main thrust of the disease growth by caution, fewer close social interactions, and even retirement.
The lockdown dramatically changed this balance between young and old.
The lockdown dramatically changed this balance between young and old.
6/ Just 8 days after the lockdown began, live symptomatic cases (shown by the app, first tweet in this thread) peaked at about 2.1 million before dropping steeply to 360,000 by 23rd April. What had changed? Rapid transmission between the socially active young had almost ended.
