Nearly a quarter of school staff are having to stay at home in order to protect themselves or a member of their household, owing to pre-existing medical conditions or pregnancy, according to a snap poll by the NEU teaching union.
In the survey of more than 2,000 mainstream school staff, 23 per cent said they were currently shielding to protect themselves or their household members because of underlying medical vulnerabilities or pregnancy.
The proportion is higher in London (28 per cent) and the situation raises questions about how many teachers would be available to work in schools if they were opened to more pupils.
Nealry one-third of teachers – 30 per cent – had spent time in self-isolation since lockdown was imposed. This figure was higher amongst respondents in London (36 per cent).
The findings were published on the day that more than three-fifths of headteachers said a lack of available staff could prevent schools from reopening to more pupils.
Of the 1,931 respondents to the NEU survey who are working regularly in schools, three-fifths of teachers were concerned about social distancing measures for pupils.
Sixty-one per cent reported they were "concerned" or "very concerned" about social distancing measures in their schools for pupils, at a time when just 2 per cent of pupils are in attendance.
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And 50 per cent reported being concerned over similar social distancing measures for staff, with one in five reporting that they were "very concerned".
Just 11 per cent of the group working in schools currently said their school was conducting temperature checks for staff or students, and 22 per cent reported that their school lacked sufficient hand soap or hand sanitiser, with no routine washing of hands at their schools.
NEU leaders said there should be no "mad rush" to reopen schools.
Kevin Courtney, joint general secretary of the NEU, said: “Teachers, heads and support staff have been working hard since mid-March to support each one of their pupils, whether at school or remotely.
"Throughout this time school leaders have done their level best to ensure the safety of staff and pupils alike, but this can only go so far. It is clear from the findings of this survey that much more needs to be done to equip schools for the road ahead.
“With thousands of new cases of Covid-19 announced each day, the government is being premature in its off-the-record briefings about school reopenings.
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"We have written repeatedly to the government to get them to reveal their modelling of the spread of the virus in schools and what measures they are planning to mitigate the obvious risks for adults working in schools, as well as children’s families, particularly those living with vulnerable relatives. We have not yet received any reply.
“There should be no mad rush to reopen schools. It must be done with great care, and alongside a profession who feel confident about safety measures being adequate and fit for purpose.
"Parents also agree with us – they have shown immense patience in recent weeks, for which all school staff are grateful. But that goodwill and effort from the public will be squandered by returning pupils too hastily. Safety must come first.
“We need to see evidence of a sustained downward trend in cases, a national plan for social distancing and PPE [personal protective equipment], comprehensive access to testing for staff and pupils and a whole-school strategy for when cases emerge before plans can be made to open schools on a wider basis than at present.”