Long COVID is rare in children who overcome the coronavirus, research suggests.
Not everyone who fights off the infection returns to a clean bill of health, with at least one in 10 adults enduring lingering complications despite testing negative for the virus itself.
Long COVID has been reported after mild or asymptomatic cases of the coronavirus. With children rarely becoming seriously ill with the infection, scientists from King's College London investigated the prevalence of lingering complications in young people.
After analysing 1,734 children – aged five to 17 – who had tested positive for the coronavirus, the team found most recovered within one week.
Just under one in 20 (4.4%), however, were enduring symptoms like fatigue, headaches and a dampened sense of smell one month later.
The results – published in The Lancet Child & Adolescent Health journal – also reveal almost all (98.2%) of the children had made a full recovery at eight weeks post-infection.
Watch: What is long COVID?
"It is reassuring the number of children experiencing long-lasting symptoms of COVID-19 [the disease caused by the coronavirus] symptoms is low," said lead author Professor Emma Duncan.
"Nevertheless, a small number of children do experience long illness with COVID-19 and our study validates the experiences of these children and their families."
Long COVID has been defined as "signs and symptoms that develop during or following an infection consistent with COVID-19 and which continue for more than four weeks, and are not explained by an alternative diagnosis".
The extent to which the condition affects children was unclear, with studies throwing up mixed results.
Infected children often develop no coronavirus symptoms. The King's study's 1,734 participants, however, all showed signs of the infection around the time they tested positive.
The study period spanned from September 2020 to February 2021 – coinciding with the reopening of schools and the peak of the UK's winter wave, when testing was widespread.
The children's symptoms were regularly reported by their parent or carer via the Zoe COVID Study app until the youngster became healthy again.
The children typically endured three symptoms, which resolved within six days. Of the 4.4% who were still ill at four weeks, most had just two symptoms.
Among adults, the coronavirus is known to become more severe with age. In the King's study, the children aged 12 to 17 were typically unwell for one week, versus five days among the five to 11 year olds.
When it comes to long COVID, 5.1% of the older children had symptoms after four weeks, compared to 3.1% of those of a primary school age.
At eight weeks, however, long COVID equally affected children of all ages.
According to co-author Dr Erika Molteni, "nearly a quarter of symptomatic children testing positive for [the coronavirus] did not report core symptoms" – defined as a fever, cough and muted senses by the NHS.
In addition, the children with the coronavirus were ill for twice as long as those who were suspected as having other illnesses, like colds or flu – at six days versus just 72 hours.
Less than one in 100 (0.9%) of the children who endured other illnesses, but tested negative for the coronavirus, were still unwell four weeks later.
These 0.9% had on average five symptoms, however, versus just two symptoms among the long COVID patients.
"Our data highlight that other illnesses, such as colds and flu, can also have prolonged symptoms in children and it is important to consider this when planning for paediatric health services during the pandemic and beyond," said co-author Dr Michael Absoud.
"This will be particularly important given that the prevalence of these illnesses is likely to increase as physical distancing measures implemented to prevent the spread of COVID-19 are relaxed."
The scientists have stressed they did not cross-check the reported symptoms with the children's health records. The parents or carers may have also varied in how they reported these symptoms.
The King's results suggest long COVID is less common in children than figures from the Office for National Statistics (ONS) have implied.
The ONS data released in April, 2021, suggest just under one in 10 (9.8%) children aged two to 11 and 13% of those between 12 and 16 had ongoing symptoms five weeks after testing positive for the coronavirus.
Differences in how long COVID was defined and the information was collected may explain the discrepancy.
Co-author Professor Emma Duncan concluded: "We hope our results will be useful and timely for doctors, parents and schools caring for these children – and of course the affected children themselves."