Teachers have been told to “be vigilant” about Covid-19 safety as a report shows the majority of outbreaks in reopened English schools were among staff rather than pupils.

There were 30 outbreaks of coronavirus in English schools after the easing of national lockdown, according to a Public Health England (PHE) report.

The report, published on Sunday, said the reopening of schools was associated with a total of 198 confirmed Covid-19 cases - 70 in children and 128 in staff.

The majority of cases linked to outbreaks were among staff, said the report, which warned that staff need to be “more vigilant” regarding exposure outside of school.

The warning has been emphasised by Dr Shamez Ladhani, paediatric infectious diseases specialist at PHE, who headed the monitoring of England’s schools.

Dr Ladhani told The Times: “We need to educate the educators.

“There’s a clear need for a duty of care outside the school setting so staff need to protect themselves, and in turn other staff and pupils.”

He added: “Staff are very good at social distancing and infection control in the classroom, but upon leaving the school environment these measures are more likely to be broken, potentially putting themselves and their colleagues at risk.”

There were 67 single confirmed cases, four “co-primary” cases and 30 outbreaks of Covid-19 in schools during June, it added.

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Co-primary cases were defined as two or more confirmed cases with a common epidemiological link diagnosed at the same time, while outbreaks were defined as two or more epidemiologically linked cases where subsequent cases were diagnosed within 14 days.

Outbreaks were usually small in size and more than half (53 per cent) involved just one secondary case, the analysis said.

The report said there was a “strong correlation” between community coronavirus incidence and risk of outbreaks in educational settings, even during a period of low Covid-19 incidence.

But it added this was not surprising because increased community transmission provided more opportunities for the virus to be introduced into educational settings.

The analysis said further school closures may be necessary in regions with increasing community infection, but this should only be considered “in extremis”.

It said: “The potential for spread within educational settings, as observed from the wider swabbing of some schools in our surveillance and from recent reports from other countries, does suggest that school closures may be necessary as part of lockdown in regions with increasing community infection, although given what is known about the detrimental effects of lack of access to education on child development, these should probably be considered only in extremis by comparison with other lockdown measures.”

Education settings in England were asked to reopen to children in nursery, Reception, Year 1 and Year 6 at the start of June, extending to Year 10 and 12 students from 15 June, the analysis said.

But it said the reopening was not mandatory and was met with “mixed responses”, with only 1.6 million of the 8.9 million pupils nationally attending any educational setting during the “summer mini-term”.

Paul Hunter, professor in medicine at the University of East Anglia, said it was difficult to extrapolate the findings from the study - which was done when a lot of children were not in school and a majority of those attending were under 11 - to the autumn, when schools are due to fully reopen.

He added: “Whilst there is still uncertainty over the science we certainly cannot discount schools as a likely accelerator of the epidemic in the wider community. 

“Nevertheless I think Professor (Chris) Whitty is correct when he says that missing schools is worse for children than the virus.

“The DHSC [Department of Health and Social Care] has produced guidance to schools and if this is followed this should help reduce the risk.

“However, once schools return and if the general incidence in the UK increases we are likely to see many more school-based outbreaks with considerable disruption this autumn.”

The analysis also said the majority of cases linked to outbreaks were in staff and warned staff need to be “more vigilant” for exposure outside the school.

It found that in half of the 30 confirmed outbreaks, the “probable transmission direction” was staff-to-staff, with seven staff-to-student, six student-to-staff and two student-to-student.

But it said early detection and isolation of staff and students can prevent the progression of an outbreak “in most cases”.

It added: “Within the educational setting, the higher risk of SARS-CoV-2 among staff highlights a need to strengthen infection control measures at two levels.

“Staff members need to be more vigilant for exposure outside the school setting to protect themselves, their families and the educational setting.

“Within the education premises, stringent infection control measures between staff need to be reinforced, including use of common staff rooms and cross-covering staff across bubbles.”

The analysis comes the day after the UK’s chief medical officers warned children are more at risk of long-term harm if they do not attend school than if they return to the classroom despite coronavirus.

Kevin Courtney, joint general secretary, of the National Education Union, said schools and colleges needed to know what should happen if an outbreak of the virus occurs in individual schools or through national, regional or local spikes.

He said the government needed to issue guidance on moving to teaching rotas or limited openings and to hire more teachers to allow education to continue if infection rates rise.

Mr Courtney added: “Government advice needs to cover the possible self-isolation of bubbles and, in extremis, moving to rotas or to more limited opening.

“It needs to cover advice to heads about the protections needed for staff in high-risk categories if infection rates rise.

“The government should be employing more teachers and seeking extra teaching spaces to allow education to continue in a Covid-secure manner if infections rise.”