Estimating Long COVID

What is the prevalence of this post-COVID syndrome?

Prof Anthony Costello (UCL) gave evidence to an all-parliamentary group of MPs. The social media account for this all-parliamentary group summarised his contribution:

The worry is this — we do not really understand Long Covid and what it means. We don’t know how long this lasts in people’s bodies. There is a lot to be concerned about.

There are 19 million children in the UK. If we just let them remain un-vaccinated, half of them become infected. That is 9.5 million[.] If 15% or 13% get prolonged symptoms, that could mean 1.3–1.5 million children.

This article looks at estimations of Long COVID, and the claim about the number of children in the UK.

What is ‘Long COVID’?

Some people who contract COVID-19 may experience symptoms for a long time. The National Health Service website states:

Emerging evidence and patient testimony is showing a growing number of people who contract COVID-19 cannot shake off the effects of the virus months after initially falling ill.

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In some patients, the virus casts a long shadow. (Image: Lockton Interational)

The Office for National Statistics conducts an infection survey, testing for SARS-CoV-2. This is the virus that causes COVID-19.

After five weeks, the estimated share of young people reporting symptoms is:

  • Age 2–11 years: 12.9% (10.4% — 16.0%)
  • Age 12–16 years: 14.5% (11.7% — 17.9%)

This survey appears to the source for the “15% or 13%” figures. For all people, the symptomatic share after five weeks was 22% (21% — 23%).

The symptoms include fatigue, coughs, headaches, fever, loss of taste, and loss of smell. There is also myalgia, sore throat, breath shortness, nausea, diarrhoea, and abdominal pain. The survey estimate is between 22nd April and 14th December 2020.

5 and 12 weeks

The ONS compared post-infection symptoms at two different cut-offs:

  • Symptomatic at 5 weeks: 21.0% (19.9% — 22.1%)
  • Symptomatic at 12 weeks: 9.9% (6.7% — 14.7%)
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Around 1 in 10 infected people report having symptoms 12 weeks later. (Image: ONS)

In these tables, there is not a breakdown into age groups. This is using a different period (ending 7th December).

Measurement of post-COVID syndrome will involve discussions defining “prolonged” symptoms. The ONS infection survey series suggests symptoms wane over time. Part of that decrease could be attrition. Researchers may be unable to contact some people for follow-up questions.

Another problem is the commonality of some symptoms. Headaches and fatigue can be signs of stress. There is also some overlap with symptoms of a common cold. For comparison, we need to understand what children without a positive test experience.

On 1st February, the ONS published an update on their estimation method. The paper highlights the addition of a new question about long COVID-19 symptoms.

The number of UK children is under 15 million

The ranged estimate involves a calculation error.

This 19m number is too high.

There are not 19 million children in the UK.

According to the ONS mid-year population estimates for 2019, there are:

  • about 14.9 million people aged 18 or under in the UK;
  • or around 13.4 million aged 16 or under.

The suggested range understates the uncertainty involved. This range is illustrative: based on an assumption 50% of children become infected.

Since this is a novel virus, studies of post-disease syndromes are in their infancy. We need to learn more.

Edit: I added a reference to the ONS paper about their estimation method.

This blog looks at the use of statistics in Britain and beyond. It is written by RSS Statistical Ambassador and Chartered Statistician @anthonybmasters.

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