Schools do not play a major role in spreading the coronavirus, according to the results of German research.
The study, the largest carried out on schoolchildren and teachers in Germany, found traces of the virus in fewer than 1 per cent of teachers and children.
Scientists from Dresden Technical University said they believe children may act as a "brake" on chains of infection.
Professor Reinhard Berner, the head of paediatric medicine at Dresden University Hospital said the results suggested the virus does not spread easily in schools.
"It is rather the opposite," he said.
"Children act more as a brake on infection. Not every infection that reaches them is passed on."
The study tested 2045 children and teachers at 13 schools in Saxony - the only German state to controversially reopen schools with full class sizes in May - but scientists found antibodies in just 12 of those who took part.
"This means that the degree of immunisation in the group of study participants is well below 1 per cent and much lower then we expected," Berner said.
"This suggests schools have not developed into hot spots."
Saxony's regional government ordered the study to determine whether the policy to reopen schools had been right.
Full class sizes are set to resume at schools across Germany after the northern summer holidays.
Researchers found 24 of those who took part in the study had family members who had tested positive for Covid-19 but only one of them was found to have developed antibodies.
"This means the majority of schoolchildren do not get infected themselves despite an infection in the household," said Berner.