Younger children who went to school during lockdown were at no greater risk of contracting Covid-19 than those staying at home, a study suggests.

Scientists detected only three positive cases out of more than 12,000 pupils and staff tested in primary and pre-schools across England in June and July, according to the Public Health England (PHE) report.

All three cases – two staff and one pupil – were mild or asymptomatic, and there was no evidence of onward transmission to household contacts or the wider education setting, the research suggests.

The preliminary findings of the PHE study have been published as thousands of pupils in England and Wales have begun returning to school full-time, with the remainder due to open their doors next week.

But the findings cannot be extrapolated to secondary schools because the risk of Covid-19 “exposure, asymptomatic infection and symptomatic disease in teenagers is likely to be different,” the report adds.

This is the largest study of its kind in the country and suggests attending preschool and primary school brings no additional risk to either staff or students

The Covid-19 Surveillance in School Kids (sKIDs) study took swabs from 12,026 adults and children in order to test them for coronavirus in 131 English primary and preschools before the summer break.

The study – which separately tested a sample of participants in five regions for antibodies – also found that the levels of antibodies were consistent with levels detected in the general population.

Antibodies were more likely to be detected in pupils and staff from black and minority ethnic groups, in those with a healthcare worker as a parent or in the household, and in children with a history of being unwell with Covid-19 symptoms, the PHE report found.

From June, primary schools in England opened their doors to children in nursery, Reception, Year 1 or Year 6 as lockdown measures were eased.

Children in all year groups are returning to the classroom full-time this month after schools and colleges closed nearly six months ago due to Covid-19.

Education Secretary Gavin Williamson said: “I am hugely encouraged by the findings of this report, which support what the UK’s chief medical officers have already made clear – that the risk of catching coronavirus at school is low, meaning that the risk to children being out of school is, in fact, far greater.

“This week has seen thousands of children reunited with classmates and teachers as schools across the country begin to reopen for full-time education for all pupils at the start of the autumn term.

“Parents can be reassured that schools have in place protective measures to reduce the risk of transmission and these findings add to the assurance that the return to school has been based on the best scientific and medical advice.”

We must not be complacent and falsely reassured

Dr Shamez Ladhani, a consultant epidemiologist at PHE, said: “This is the largest study of its kind in the country and suggests attending preschool and primary school brings no additional risk to either staff or students.

“Although these results are preliminary, they should be very reassuring to parents who may be anxious about their children returning to school.

“As has been found in previous research, infection within educational settings is extremely low, and while it appears that children do contract Covid-19, the overwhelming majority experience mild or no symptoms, and are unlikely to pass it on.”

On the findings, Ravindra Gupta, professor of clinical microbiology at the University of Cambridge, said “some cautious optimism is needed”.

“This was conducted in schools with limited numbers of children attending, three year groups at most,” he said.

Professor Gupta added: “From September, there will be more children, more mixing, more crowding and over winter less time will be spent outdoors. There is less ability to socially distance than schools were able to in June.

“We must not be complacent and falsely reassured. We must ensure adequate monitoring and testing strategies to pick up infections in schools before they spread.”