The most commonly reported symptoms among children 0-3 years old were mood swings, rashes and stomach aches.
In the study, researchers from Copenhagen University Hospital, Denmark analysed data from a survey of 11,000 children aged 0-14 with a positive Covid-19 test result between January 2020 and July 2021, and were then matched by age and sex to over 33,000 children who never had tested positive for Covid.
Among 4-11 years old the most commonly reported symptoms were mood swings, trouble remembering or concentrating, and rashes, and among 12-14 years old, fatigue, mood swings, and trouble remembering or concentrating.
The results of the study found children diagnosed with Covid-19 in all age groups to be more likely to experience at least one symptom for two months or longer than the control group.
In the 0-3 years age group 40 per cent of children diagnosed with Covid-19 (478 of 1,194 children) experienced symptoms for longer than two months, compared to 27 per cent of controls (1,049 of 3,855 children).
For the 4-11 years age group the ratio was 38 per cent of cases (1,912 of 5,023 children) compared to 34 per cent of controls (6,189 of 18,372 children), and for the 12-14 years age group, 46 per cent of cases (1,313 of 2,857 children) compared to 41 per cent of controls (4,454 of 10,789 children) experienced long-lasting symptoms.
"Our findings align with previous studies of long Covid in adolescents showing that, although the chances of children experiencing long Covid is low, especially compared to control groups, it must be recognised and treated seriously," said Professor Selina Kikkenborg Berg from the hospital.
Approximately one third of children with positive Covid-19 tests reported experiencing symptoms that were not present before the SARS-CoV-2 infection. In addition, with increasing duration of symptoms, the proportion of children with those symptoms tended to decrease.
"Knowledge of long-term symptom burden in SARS-CoV-2 positive children is essential to guide clinical recognition, parental caregiving, and societal decisions about isolation, lockdown, non-pharmaceutical interventions, and vaccine strategies," Berg noted.