Around two-thirds of children under 12 have already been infected with coronavirus, scientists have estimated after studying more than 300 families.

People who developed cold or flu-like symptoms were asked to keep diaries of their symptoms and take PCR tests to see if they had the virus or another illness.

The study of 1209 people, including 582 children, ran from September 2020 until June this year and was run by Utrecht’s UMC teaching hospital.

Based on the figures the researchers calculated that between 20% and 40% of the children contracted the virus in a year, which they extrapolated to two-thirds of all children in the time since the pandemic began.

Most young children developed only mild symptoms, similar to a cold. However, the study mostly covered the period before the more infectious and severe Delta strain emerged.

Head researcher Patricia Bruining said: ‘Obviously we have known for a while that children become less sick than adults from coronavirus, but the good thing about this study is that we can now show how the viral infection develops based on highly detailed data about symptoms.

Bruijning said the findings indicated that more children had had coronavirus than previously thought. ‘The last serological investigation was in June 2021, when it looked as if between 25% and 30% of children had antibodies in their blood. That figure has been used as the standard.’