Long-lasting symptoms from Covid-19 are rare in children, with the illness typically lasting an average of six days in this cohort, a new study has found.

Many children who develop Covid-19 are asymptomatic and those who develop symptoms tend to only experience a mild illness. Researchers from King’s College London in the UK set out to assess the potential impact of ‘long Covid’ on children.

Long Covid refers to a prolonged illness after infection with the SARS-CoV-2 virus, which sees symptoms lasting longer than four weeks.

The researchers used data collected through the ZOE COVID Study smartphone app, which includes data from more than 250,000 UK children who are aged between five and 17 years. Covid symptoms were reported through the app by parents or carers.

The researchers focused on reports collected between September 1, 2020 and February 22, 2021. During this time, 1,734 children developed symptoms of Covid-19 and received a positive PCR test result close to the onset of symptoms. These symptoms were then reported regularly until the children were healthy again.

This meant that the researchers could accurately attribute these children’s symptoms to Covid-19 and could assess illness duration robustly.

The study found that overall, children were ill for an average of six days and experienced an average of three symptoms in the first week of illness. This confirmed that the virus tends to manifest as a mild illness in children and recovery is usually quick.

Just 4.4% of children experienced symptoms beyond four weeks and these had an average of two persistent symptoms, typically fatigue, headache or loss of sense of smell.

However overall, 98.2% of symptomatic children recovered by eight weeks.

The study noted that older children tended to be ill for longer – the average illness duration was seven days in children aged 12 to 17 years compared to five days in children aged five to 11 years.

Older children were also more likely to still have symptoms after four weeks – 5.1% of 12 to 17 year-olds compared to 3.1% of five to 11 year-olds. However, there was no difference in the number of children who still had symptoms after eight weeks.

“It is reassuring that the number of children experiencing long-lasting symptoms of Covid-19 is low. 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,” commented the study’s lead author, Prof Emma Duncan of King’s College London.

She added that she hopes these findings “will be useful and timely for doctors, parents and schools caring for these children, and of course the affected children themselves”.

Details are published in the journal, The Lancet Child & Adolescent Health.