Doing a test in half-term before returning to the classroom could prevent onwards spread, experts advise.
Young people are being urged to do a rapid Covid test before they return to school after half-term. to prevent more new infections.
The UK Health Security Agency says cases among 10 to 19-year-olds are currently the highest of any age group.
People can be contagious even if they have no symptoms and are unaware that they have Covid.
Free lateral flow kits can be collected from local pharmacies if pupils do not already have them at home.
Many pupils in England and Wales return to school next week.
Anyone who has Covid symptoms or tests positive should isolate and get a confirmatory PCR test as quickly as possible.
Rapid testing and appropriate isolation can break chains of transmission and prevent the spread of the virus, especially as we enter the winter months.
Vaccination can also help prevent cases.
The UK’s chief medical officers have recommended a single Pfizer Covid dose for all 12 to 15-year-olds.
So far the programme in England has been delivered through schools, but from half-term, teenagers will also be able to have their jab at an existing vaccination centre. Not every site will be able to see children immediately though, so families may not be able to go to their nearest centre.
Latest figures for England suggest 17% of young people aged 12 to 15 have had the jab.
Covid levels remain high in the UK, but have recently shown signs of a small fall.
A further 39,842 confirmed new Covid cases across all age groups in the UK were announced on Thursday.
Estimates from the ONS infection survey suggest that 1.3 million people in the UK would test positive for coronavirus in the week ending 22 October.
That is 1.9% of the population, or one in 55 people – up from one in 60 the previous week.
Chief executive of the UK Health Security Agency, Dr Jenny Harries, said: “I am calling on all children to help themselves and each other by getting tested before going back to the classroom, so that we can stop the infection in its tracks and keep as many children in the classroom as possible, continuing their education and developing their futures.
“I want to once again thank all our teachers and those who work in schools who are working so hard to help keep children safe.”
Education Secretary Nadhim Zahawi said: “As we start the countdown to Christmas, testing regularly and getting vaccinated is the best thing we can all do to protect education and make sure we can enjoy the best of the season – whether that’s the school nativity or the family gathering over the holidays.”
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