Transmission of Covid-19 in primary schools was “extremely low” and outbreaks were rare during the autumn, Public Health England (PHE) has said.
The latest study found a “very low risk” of infection in both students and staff in primary schools after pupils in England returned to class from September.
But the paper concludes that similar studies are needed in secondary schools and universities where the risks of infection are likely to be different.
Dr Shamez Ladhani, a PHE consultant paediatrician and study lead, said: “Evidence gathered from primaries during the autumn term suggests transmission in primary schools is extremely low and outbreaks are rare.
“There is also very little evidence students or staff are spreading the virus asymptomatically within primaries.”
He added: “Schools should be the first setting to reopen when it is safe to do so, and we are carefully monitoring the data.”
The findings come as Conservative MPs called for schools to be reopened after the February half-term in areas where Covid-19 infection rates are low.
Schools Minister Nick Gibb said the Government will be led by the science when making decisions about “moving away from the lockdown conditions”, but he added that reopening schools will remain a priority.
Vaccines Minister Nadhim Zahawi said studies about infection rates at primary schools had been encouraging.
He told BBC Breakfast: “The infection rates are much lower among primary school children than secondary – I think it is five times higher in secondary schools.
“I think once we see the national infection rates continue to drop – we still have 37,000 people in hospital with Covid, but once we get to a place where schools can be safely reopened, it will be the first thing we do.”
Pupils in schools and colleges in England, except children of key workers and vulnerable pupils, have been told to learn remotely as part of the lockdown.
The latest Government data shows that the number of children of key workers in schools in England during the lockdown has dropped in the past week.
Approximately 813,000 children of critical workers were in attendance on January 21, down from 820,000 on January 13. This represents 71% of all pupils in attendance at school last week.
But the overall proportion of pupils in class (14%) remains the same as the week before, according to figures from the Department for Education (DfE).
More than a fifth (21%) of primary school pupils were on-site last week, while 5% of secondary school students were in class – the same as on January 13.
The percentage of pupils with an education, health and care plan (EHCP), or with a social worker, in class has risen slightly on the week before.
New figures from the DfE show that an additional 74,489 laptops and tablets have been delivered or dispatched by the Government to help with remote learning in the past week.
Education Secretary Gavin Williamson said: “We continue to provide devices at huge speed and scale for those children who need them the most, with over 875,000 now delivered to schools and councils.
“Over 300,000 of these have been delivered since schools closed to most pupils, helping ensure no child loses out while learning at home.
“I want to thank teachers, school staff and parents who continue to work tirelessly to ensure vulnerable and critical worker children can still attend school, while delivering remote education for those at home.”