Covid Watch 104: Cases are growing among younger people in Shropshire as the nation heads towards an even tighter lockdown (updated)

Covid Watch 104: Cases are growing among younger people in Shropshire as the nation heads towards an even tighter lockdown (updated)

It’s quite hard to a grip on the details of the coronavirus epidemic at times. The headline figures hide a lot of detail. In this article, we concentrate on infection by age group within Shropshire. Before the holiday, Shropshire infection rates were dropping. That is in stark contrast to England as a whole. Particularly Tier 4 areas in the south and east and in South Wales. The soaring infection rates across the country are driven by the faster spreading new variant of Covid. It’s scary. Very scary.

The latest data for our locality gives us an insight into the age profile of those testing positive for Covid-19 in Shropshire. The over eighties, considered the most vulnerable age, still have worryingly high infection rates. But the highest rates are among people in their twenties through to their fifties. The most socially and professionally mobile age group in our population.

This article is largely based on the government’s heatmaps for infection rates by age. The heatmaps are detailed and are reproduced towards the end of this article. We’ve summarised the data in a couple of graphics.

The chart above shows the proportion of tests by age group. Over the last few months, around one third of the positive test results in Shropshire have been for the 35 to 54 years age group. A quarter of the people testing positive were 20 to 34 years of age.

Whether children should return to school next week is being debated across the media today. In Shropshire, just 7% of positive tests were in the school ages of 10 to 19 years.

We get more information when we look at infection rates in different age bands. The table below shows the average seven day infection rate per 100,000 people for each month in Shropshire since the epidemic began (see notes at the end of this article for technical details).

Average seven day infection rate by month and age

There is no formal threshold for an infection rate becoming a matter of concern. But a seven day infection rate above 100 is widely regarded as worrying and a trigger for increased action.

The highest rates in Shropshire have been in the 20 to 34 years age bracket. If that age group lived on its own geographically, it would probably be in Tier 3 by now. But the cohort doesn’t live on its own and cross infection is occurring between age groups.

Whether children should return to school is the debate of the day. In Shropshire, the secondary school age cohort has had high detected infection rates during the second wave but not as high as people who are 20 to 54 years of age. Many of this older group will of course be parents.

The difficulty with a disease that thrives on sociability is that we don’t know who is infecting who. It has no respect for age but has the greatest impact on people whose health is vulnerable and, overall, vulnerability increases with age.

National attention is focused on the new variant of Covid-19 which could be 70% more transmissible. We don’t know if this has got to Shropshire yet but with the increased social mixing over the festive period it will be here. It will be everywhere.  

Daily reports of the number of Covid-19 positive tests are never precise and are adjusted over five days. But the national trend cannot be hidden behind minor adjustments. It is soaring. A plane taking off rather than a plane gliding in to land.

Shropshire tends to lag around a week to ten days behind the more populated areas of England in Covid trends. That’s a more comfortable place to be. So far, we have not caught up with the national scene. We have experienced a lower infection rate throughout the epidemic. We need to keep it that way.

Update 30 December 2020

Internet problems yesterday meant I could not include some graphs that illustrate the theme of this article. I include then now. As I type, the Independent Sage group is warning in an online briefing that the new variant is spreading faster among children than the original virus strain.

Note the vertical axis above is 0-300. The axis is 0-400 in the two graphs below.
Heatmap for Shropshire infection rates by age
Heatmap for Telford infection rates by age
Heatmap for England infection rates by age

Technical notes

Covid cases during the first wave were underreported due to a lack of testing. Until testing was made widely available in the mid-summer, testing often concentrated on older people. The government did not include all test data in reports until 2 July.

Tests only partly record the prevalence of Covid-19 in the community. Many people are asymptomatic carriers are not tested. Some age groups can more easily access tests than others.

The seven day infection rate in the table is the average over the month calculated by dividing the monthly infection rate per 100,000 by the number of days in the month (the number of days for which data are available for March and December) and multiplying by seven.

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