Some schools have had to bring back Covid-like measures to prevent the spread of flu, as rates of reported illnesses in schools and other educational settings are higher than this time last year.

One primary school in Leeds said last week it had to cut back on singing in assemblies and introduce sanitisation stations, while another in Caerphilly had to close temporarily.

Flu season has come early this year and some hospitals have asked staff, patients and visitors to wear face masks.

The Association of School and College Leaders said they were aware of winter illnesses causing disruption in “several schools across the UK”.

The Department for Education (DfE) in England said school closures “should only happen in extreme circumstances”.

The most recent data from the UK Health Security Agency (UKHSA), which monitors the spread of winter viruses, found there were 107 acute respiratory incidents in educational settings in England between 24 and 30 November.

An “acute respiratory incident” is defined for a school as two or more cases occurring among pupils within a five-day period. It could apply to a range of respiratory illnesses like influenza, RSV, covid or the common cold.

Of the 107 incidents reported in education settings for the last week of November, 17 identified influenza as the virus involved, with two more schools reporting Covid as the cause. In 76 cases the school didn’t know which respiratory infection was affecting them.

In comparison, during the same week last year there were only 15 respiratory incidents in educational settings overall, with only one due to influenza.

Flu is on the rise in the UK, according to the UKHSA – with a weekly average positivity rate of 17.1% among reported test results as of 2 December, up from 11.6% the week before.

A new strain of the virus, the H3N2 “subclade K” variant, is circulating. It is a mutated strain of the seasonal influenza A virus and people have not encountered much of it in recent years. That means there is less built-up immunity against it.

DfE guidance published in October asks schools in England to open windows and doors whenever possible to make sure classrooms are ventilated, and to use carbon dioxide monitors, if they have them, to “identify poorly ventilated areas”.

“Explain why you are opening the window, even on a chilly day, even just for 10 minutes can make a big difference, and the benefits of bringing fresh air into the classroom,” it says.

It also advises on reminding children of the importance of handwashing and vaccinations.

Pupils from reception to Year 11 in England are eligible for a flu vaccination nasal spray at their school.

Parents with younger children aged two and three can book their children flu vaccinations at a GP practice.

The guidance stresses the importance of attendance and says most mild illnesses, like runny noses and sore throats, do not mean children need to be off school.

But it adds that “parents know their child best” and that schools can put measures in place to reassure them.

Pepe Di’Iasio, general secretary of the Association of School and College Leaders, said: “We’re aware that flu and other winter illnesses are causing disruption in several schools across the UK and that this can be an extremely difficult situation to manage.”

He said schools would communicate any steps they were taking to parents and students and it “may necessitate the closure or partial closure of a site where the situation is particularly severe”.

“Schools always endeavour to avoid any disruption to learning and will have in place support for students who are affected”, he added.

In a statement, a DfE spokesperson confirmed that flu cases are at very high levels this year and acknowledged that it would be a “tough winter” for the NHS.

“School attendance is critical for children’s life chances, and while it’s clear cases of flu are going to have an impact on attendance levels, we are clear school closures should only happen in extreme circumstances,” they said.

“We provide clear guidance to help parents know exactly when to keep children home, and to help schools both manage children’s wellbeing and keep disruption to a minimum.”