Extrapolating figures around long Covid in kids is not the way to go
15 March 2021
What was claimed
74,000 children are living with ‘long Covid’.
The ONS figures that these estimates are based on are ‘experimental statistics’ which have measured prevalence of some long Covid symptoms in children at five weeks after infection. They shouldn’t be used as an absolute measure from which to extrapolate population levels of long Covid in children.
“More than 74,000 children’ suffering from long Covid months after infection”
Metro, 8 February 2021
“Almost 500,000 UK children are known to have had Covid – suggesting around 74,000 have had Long Covid.”
The Daily Mirror, 6 February 2021
There has been a lot of discussion recently about the prevalence of ‘long Covid’ in children, and readers have asked us about the numbers that are being discussed.
Long term effects of Covid-19 infection are increasingly being seen in children, and there is ongoing research about what exactly long Covid is, how it is caused, who is likely to experience it, and how prevalent it is.
Given all of these unknowns, we need to be cautious of claims about exactly how many children have long Covid. For example, severaloutlets have claimed that 74,000 children are suffering from long Covid.
Nuffield Professor of Child Health and Honorary Consultant Paediatrician, Sir Terence Stephenson, is leading a research project into long Covid in teenagers. He told Full Fact:
“I would be very wary of putting a figure on how common long COVID is in young people. Uncertainties relate to diagnosis, prevalence, duration and treatment of post-COVID syndrome (‘long COVID’) in children and young people (CYP). There is no diagnostic test nor definition for long COVID.
“Because there is no diagnostic test or code for long COVID, it may not be captured in routine NHS administrative datasets. Long COVID may be coded as a number of different conditions or symptom clusters in non-hospitalised CYP. It is possible that the symptoms described may be due to a mixture of factors related to the COVID pandemic, including social isolation, anxiety and depression or educational concerns - with or without evidence of actual COVID infection.”
Where did the figure come from?
The figures come from experimental estimates from the Office for National Statistics (ONS) using the results of the UK Coronavirus Infection Survey which looked at how many people still showed certain symptoms five weeks after infection. These estimates showed that 12.9% of respondents aged between 2 and 11, and 14.5% of those between 12-16 reported symptoms of fatigue, cough, headache, loss of taste or smell or myalgia (muscle aches) at five weeks after infection during the period April-December 2020.
This data is really useful to highlight the potential scale of the issue, and to start to inform conversations about supporting children around Covid-19.
The 74,000 figure quoted by the Metro and the Mirror is also widely cited by the parent and patient led advocacy and support group Long Covid Kids, who claimed in early February 2021 that 74,400 children in England were suffering from Long Covid.
A figure of 74,000 would suggest over 490,000 children in total at the time had tested positive for SARS-CoV-2 (the virus that causes Covid-19). At the time of writing there were around 546,000 0-19 years olds in England who have tested positive.
However, extrapolating from this data to say that 74,000 children are living with long Covid (by applying these percentages to the rolling number of children who have swabbed positive for SARS-CoV-2), and some of the other claims which generalise the figures, miss a few important points about the data.
Firstly the ONS have stated that these are ‘experimental estimates’, meaning that they are in the testing phase and not fully developed. This particular data set is based on 9,063 respondents of all ages, we do not yet know how many of these are children.
Professor Kevin McConway, Emeritus Professor of Applied Statistics at The Open University commented on the equivalent data set from the ONS for adults and said: “It’s good that ONS have begun to use data from their Infection Survey to give a national picture of what’s been called ‘long COVID’ [...]However, this first publication of data is limited, and, as ONS write in the Statement that accompanies the estimates, “the analysis is very much a work in progress”.
“Some of the details that I’d expect to have seen in reporting results like this, such as numbers of people still being followed up at various times after their initial infection, and numbers of patient-years at risk for the adverse events that are considered, are not published in this release. The plans for further work and further analysis, outlined in the Statement accompanying the numbers, look promising, but it’s much too early for me to judge how they will work out.”
Some medics have expressed caution about using the data in this way for a number of other reasons. Firstly, as described by Sir Terence Stephenson, we do not yet have a clear definition for long Covid in children, and the definition varies greatly even for adults. For example, some sources consider long Covid in adults to be symptoms beyond 3 weeks after first displaying symptoms, others such as the National Institute for Health and Care Excellence (NICE) describe symptoms at 4-12 weeks as ‘ongoing symptomatic Covid-19’ and a ‘post Covid-19 syndrome’ if symptoms persist beyond 12 weeks of infection. Some of the children who reported an individual symptom in the ONS survey at 5 weeks after infection may not be experiencing the debilitating chronic syndrome that the term long Covid evokes and may simply be reporting one of the quite common symptoms included in the questionnaire.
In addition, paediatricians have commented on the need to compare these figures to a control group who have not had Covid-19 to see how common these kinds of symptoms are generally in children. For example pre-pandemic, a 2017 cohort study of 7,670 children in Leicestershire showed a 34-55% prevalence of cough without cold depending on age.
Particularly amidst the stress of the Covid-19 pandemic, some of the symptoms could be more common in children at the moment, regardless of whether or not they have had Covid-19. Sir Terence Stephenson’s research for example, will follow 3,000 teenagers who have tested positive for SARS-CoV-2, and 3000 who have not over two years to compare symptom prevalence (amongst other things) between the two groups.
Saying that 74,000 children have had long Covid symptoms could also be underplaying the number of children who are experiencing these symptoms, as although they quote “500,000 children” that are known to have tested positive for Covid-19, many more may have had asymptomatic initial infections or were not tested. Children may also experience many different kinds of symptoms as a feature of long Covid which were not included on the questionnaire supplied during the collection of ONS data, for example ‘brain fog’ and neurological complaints, skin rashes, gastrointestinal problems or psychiatric symptoms.
It’s also important to recognise that people do recover from long Covid, therefore someone who experienced symptoms at 5 weeks, may well recover and no longer have a long Covid-type illness or syndrome.