Primary school-aged children infected with the coronavirus have much smaller viral loads than adults with Covid-19, a study has found. .

Rapid antigen tests, like ones suggested for use in schools and airports, are also likely to be less accurate for children than adults, due to this smaller load, the researchers say. .

'To our knowledge this is the first study to evaluate SARS-CoV-2 viral load distributions in a large number of patients from different patient categories,' the researchers write in their study, which has not yet been peer-reviewed and is published online as a pre-print. 

'Our data present a clear relation between age and SARS-CoV-2 viral load, with children (less than 12 years) showing lower viral loads independent of sex and symptom duration.'

The higher the figure, the lower the viral load, as it indicates how many cycles of amplification were required. 

'The most remarkable finding of this study was the relation between SARS-CoV-2 viral load and age, with significantly lower viral loads in children,' the study authors from Kennemerland in the north of the Netherlands add.  

The Dutch researchers point out that antigen tests, which are quicker but not as reliable as PCR tests, are even less accurate when used by an infected patient with a low viral load

In infected children younger than 12, the registered viral load was less than 30 in almost a third (31.1 per cent) of cases, almost double the proportion of people with this low reading in all other age groups. 

As a result, the researchers say 'SARS-CoV-2 antigen tests could have lower sensitivity in children than in adults'