The student age group and covid-19

During lockdown2 I've been doing some analysis of the statistics on Covid-19, using this as a pretext to learn the Python programming language. The government site at https://coronavirus.data.gov.uk is a wonderful gateway into a huge amount of data. And I have the kind of mind that finds comfort in data: knowing more about the disease than it knows about me makes me feel stronger, in some way.

The interactive map on that site (https://coronavirus.data.gov.uk/details/interactive-map) gives you a feel for how different parts of the country have different rates of infection. Zooming in, you find more surprising variations: the rate of infection in Lewisham and Bromley is significantly lower than most other London boroughs and urban areas. Hastings has a ridiculously low rate. No-one really knows why.

But you also see that there are patches of high infection. Exeter, for example, stood out. Like Cambridge and Bristol, its rate was higher than that of its neighbours. 

So I decided to look at the age breakdown of new positive tests in various areas. Here's the picture in Lewisham. In the first few months only the very ill or the elderly could get tested. From about July testing was much more widely available and the proportions of each age band stayed nearly constant even when the number of cases rose rapidly in October. (The age bands and their names are slightly arbitrary.) In October the student-age group made up about 27% of positive tests. 

But here's the comparative chart for Cambridge. In August-October the proportion of 15-24 year-olds rose enormously. (Oxford is similar.)

Exeter, another university city, is even clearer. In September-October about 75% of those tested positive were in the 15-24 age group. 

Here's the chart of numbers of cases in Exeter. There were hardly any infections before September. The vast majority of those since have been of under-25s but already in October the rate in older age groups was growing. 

Obviously, not everyone between 15 and 24 is a student, but most students are between 15 and 24. As the rate of student-age infection falls, that of over 60s increases. 

It seems clear that the return to university was a major driver of the second wave in some areas. Schools (of which there are plenty in Lewisham) maybe not so much. In all cases the number of under-15s is pretty constant. People under 25 are much more likely to survive infection, but can spread it to older generations. The October figure is probably a flare-up: most of those infected will survive but a percentage of the elders will not. 

Technical note: the figures in this analysis are based on those in https://coronavirus.data.gov.uk/downloads/demographic/cases/specimenDate_ageDemographic-stacked.csv and I'd welcome any opinions on whether I've interpreted the data correctly. The graphs are drawn in Google sheets. Thanks to Clare Griffiths (@statsgeekclare) for pointing out an error in my original calculations. I have slightly modified the results accordingly.