Long Covid symptoms rarely persist beyond 12 weeks in children and adolescents unlike adults, new research suggests.

The review found existing studies on the condition in children and adolescents have major limitations.

Some do not show a difference in symptoms between those who have been infected with the virus and those who have not.

It comes as research from the Murdoch Children’s Research Institute (MCRI) in Australia found that after 10 months in circulation, the Delta variant had not caused more serious disease in children than previous variants and most cases remained asymptomatic or mild.

It also found children and adolescents with pre-existing health conditions including obesity, chronic kidney disease, cardiovascular disease and immune disorders have a 25-fold greater risk of severe Covid-19.

A recent systematic review reported severe Covid-19 occurred in 5.1% of children and adolescents with pre-existing conditions and in 0.2% without.

MCRI Professor Nigel Curtis said while children with Sars-CoV-2 infection are usually asymptomatic or have a mild form of the disease with low rates of hospital admissions, the risk and features of long Covid were poorly understood.

He added: “Current studies lack a clear case definition and age-related data, have variable follow-up times, and rely on self- or parent-reported symptoms without lab confirmation.

“Another significant problem is that many studies have low response rates meaning they might overestimate the risk of long Covid.”

Dr Petra Zimmermann of the MCRI and University of Fribourg said symptoms of long Covid were difficult to distinguish from those attributable to the indirect effects of the pandemic, such as school closures, not seeing friends or being unable to do sports and hobbies.

The MCRI-led review analysed 14 international studies involving 19,426 children and adolescents that reported persistent symptoms following Covid-19.

The most common symptoms reported four to 12 weeks after acute infection were headache, fatigue, sleep disturbance, concentration difficulties and abdominal pain.

Prof Curtis, who is also a professor of paediatric infectious disease at the University of Melbourne and head of infectious diseases at The Royal Children’s Hospital, said it was reassuring there was little evidence symptoms persisted longer than 12 weeks, suggesting long Covid might be less of a concern in children and adolescents than in adults.

But he said further studies were urgently needed to inform policy decisions on coronavirus vaccines for children and adolescents.

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