There have been more than 1,000 clusters and outbreaks of Covid-19 in educational settings since schools fully reopened in September, scientific advisers have said.
In a new report published today, the Scientific Advisory Group for Emergencies (Sage) says there is "no direct evidence" that school transmission plays a significant role in driving up infection rates among children – but it has "low confidence" in this.
And there is "clear evidence" that outbreaks in schools can occur, the advisers say.
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The report states: "The increases in infection among children coincided with the timings of the opening of schools. Education is a major part of young people's lives, and transmission to children and young people can occur in household, community and educational settings (high confidence).
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"There is no direct evidence that transmission within schools plays a significant contributory role in driving increased rates of infection among children (low confidence)."
It adds: "There is clear evidence that individual significant outbreaks in schools can occur.
"Since schools reopened in Sept 2020, PHE [Public Health England] indicate there have been more than 1,000 clusters and outbreaks reported in educational settings (note that clusters are defined as involving two or more test-confirmed cases of Covid-19 associated with a specific non-residential setting)."
The document, dated 4 November, suggests that secondary school students played a bigger role in introducing infection into households, as the prevalence of infection in children aged 12-16 increased between September and October.
But the difference is less marked for younger children, it says.
The role of schools in community transmission "cannot be easily considered in isolation from wider measures", the paper adds, as potential increases may emerge because opening schools enables other mixing to occur – such as parents being able to go to work, or socialising after dropping off children.
Geoff Barton, general secretary of the Association of School and College Leaders, said: "This paper finds that while Covid infection rates have increased among school-age children since September, there is no clear evidence about the extent to which schools being open may drive the rate of infection.
"On the other hand, there is clear evidence of the negative educational and mental health impact of children missing school.
"In our view, the balance of risks therefore strongly remains in favour of keeping schools open and this is absolutely the right priority.
"Schools have worked extremely hard to implement and manage Covid safety controls to minimise the risk of transmission and remain open.
"It is clear that the situation with Covid remains precarious and that the government must be ready to act if further restrictions are necessary.
"However, everything possible must be done to keep schools open, and to support the staff who have done such a superb job in managing this exceptionally difficult situation."
Paul Whiteman, general secretary of school leaders' union the NAHT, said: "It is clear that whilst we are learning all the time, we are still in the relatively early stages when it comes to understanding this virus. That is particularly true when it comes to the role that schools might play in transmission.
"Government scientists have told us that, at present, there is no direct evidence that shows that children being in school is a significant cause of transmission.
"Clearly this remains a key question and it is essential that this continues to be monitored closely. We have also been told there is no evidence of a difference in the positivity rates of education staff compared to other key workers and professions, which appears encouraging.
"However, it is clear that pupils of all ages can transmit the virus to each other and to staff and we know that there have been a number of outbreaks in schools. We remain particularly concerned about the spread of the virus amongst older pupils and in secondary schools, especially given that we know that the prevalence of the virus has risen significantly since schools reopened fully.
"There are also worrying signs that older pupils could be playing a role in spreading the virus amongst family members, and this must be watched very closely.
"Overall, it remains the case that all education staff are being asked to remain on the front line and it is incumbent upon the government to do more to ensure that all pupils and staff are kept safe. Routine testing and priority access to seasonal flu jabs are just two examples of how they could do this."
Mary Bousted, joint general secretary of the NEU teaching union, said: "We are pleased that Sage has recognised the important role that schools and school-age children play in transmission of the virus.
"We have been concerned for some time that an erroneous belief that children do not play a significant role in the transmission of coronavirus was badly distorting policy. This is in spite of a clear and sharp trend in infection rates among secondary school pupils, in particular, since the start of term.
"We call on the government to play a much more active role to suppress the transmission of Covid within schools."