Children can carry coronavirus in their noses for up to three weeks, according to a South Korean study.

As children prepare to return to school this latest study could shed some light on how likely children are to spread the virus to others.

Previous studies have found the vast majority of children with the virus have mild or no symptoms.

This study, based on 91 children at hospitals and isolation facilities across South Korea between February and March, found that even among those with few or no symptoms, the virus could be found in their swabs as much as three weeks later. All of the children recovered from the virus.

Once the researchers had identified and isolated cases, the patients were repeatedly tested until the virus had cleared.

Because South Korea has carried out mass testing, including of people without symptoms, and tracked and isolated confirmed cases, the scientists had a rare opportunity to monitor children with mild symptoms or no symptoms at all.

The researchers said their data suggests that 93% of the children with Covid-19 in South Korea could have been missed “were it not for Korea’s intensive contact tracing and aggressive diagnostic testing”.

Cases of children with undetected Covid-19 are “worrisome”, they said, because these children could “facilitate the rapid spread” of the virus in the community.  

The fact they had detectable virus in their noses, the authors concluded, suggested they were capable of passing it on.

The scientists concluded that screening for symptoms fails to identify most Covid-19 cases in children and the virus is detected for an “unexpectedly long time”.

But the scientists said the “major limitation” of the study was they were not able to measure how infectious the children were and when in the cycle of the disease they were most likely to spread the virus, mainly because of South Korea’s strict quarantine and isolation strategies which minimise exposure to vulnerable people./The Telegraph