Children who become ill with coronavirus are unlikely to have long-term effects, with less than 2% having symptoms lasting more than eight weeks, research has shown.

Illness from Covid-19 lasted no more than a week on average in people aged between five and 17, according to findings from a study led by researchers at King’s College London.

The results, published in the Lancet Child and Adolescent Health journal, involved scientists looking at daily health reports logged in the Zoe Covid Study app and focused on September 2020 through to February 2021.

Of the 1,734 children reported by parents or carers with a clear start and end point to their symptoms and a positive PCR test result, just one in 50 (1.8%) had symptoms lasting more than eight weeks.

Fewer than one in 20 (4.4%) experienced symptoms for four weeks or more.

In children aged five to 11 years old, the illness lasted on average for five days, while in children aged 12 to 17 it lasted around seven days, researchers said.

Their study showed that the most common symptoms reported in children were headaches, tiredness, a sore throat and loss of smell.

Scientists said it was reassuring that there were no reports of serious neurological symptoms such as fits or seizures, impaired concentration or anxiety.

It will be reassuring for families to know that those children who do fall ill with Covid-19 are unlikely to suffer prolonged effects

Senior author Emma Duncan, professor of clinical endocrinology at King’s College London, said: “We know from other studies that many children who catch coronavirus don’t show any symptoms at all; and it will be reassuring for families to know that those children who do fall ill with Covid-19 are unlikely to suffer prolonged effects.

“However, our research confirms that a small number do have a long illness duration with Covid-19, though these children too usually recover with time.

“We hope our results will be useful for doctors, parents, and schools caring for these children – and, of course, affected children themselves.”

Researchers also assessed children who tested negative for coronavirus but who might have had other ailments, such as colds and flu.

They found that those who were ill with Covid-19 had an average of six days of illness compared with three days for children with other illnesses, although at four weeks the small number of children with other illnesses tended to have more symptoms than those who were ill with coronavirus.

Dr Michael Absoud, a senior author of the study and consultant and senior lecturer at King’s College London, said: “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.

“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.”

Health minister Lord Bethell said: “It’s encouraging to see the condition (long Covid) is uncommon among children and we will continue to provide support to those suffering the long term effects of the virus.

“Already we have opened over 80 long Covid assessment services across England, including specialist services for children and young people backed by £100 million.”

Previous analysis by King’s College London using the Zoe Covid Symptom Study showed around one in seven adults experienced Covid-19 symptoms lasting four weeks, while one in 20 were ill for eight weeks or longer.

Prof Duncan noted that as there is no current agreed definition for long Covid in children, the study was focused on the duration of illness rather than this specific condition.