The pupils and several of their family members are now self-isolating after testing positive, headteacher Kay Mountfield told parents in a letter published in the Maidenhead Advertiser.
However, the school was deemed safe to reopen to some year groups from Thursday after the headteacher consulted council and Public Health England officials.
“These cases are all linked and were acquired abroad during the school holidays,” said councillor Anita Cramer, Buckinghamshire Council’s cabinet member for education.
“The school is clean and safe to return to, and there will be a staggered start to the school year with the older students returning slightly later to allow pupils to complete the self-isolation period.”
Video posted on TikTok showed one of the school’s pupils saying there had been “virtually no social distancing” during their trip to the Greek island, according to a report in The Sun.
The outbreak comes as health officials in Scotland said they had found “evidence” of coronavirus spreading within two secondary schools in Glasgow.
Officials from the NHS Greater Glasgow and Clyde Health Board (NHSGGC) are now carrying out contact tracing at Lochend Community High School and Hutchesons’ Grammar School in the city.
A spokesperson for the health board there was “evidence of transmission of the virus amongst a small number of cases in school settings”.
Scotland’s education secretary John Swinney told the Scottish parliament that 127 pupils had contracted Covid-19 since classes started back up again on 11 August.
Meanwhile, pressure is mounting on authorities in England to consider imposing quarantine rules on travellers arriving from Greece and Portugal.
Health secretary Matt Hancock said a decision on whether to impose restrictions on the countries would be announced on Friday.
Rising Covid-19 cases prompted the Scottish government to announce travellers from Greece would have to self-isolate for 14 days from Thursday, while Wales began asking arrivals from the island of Zante to enter quarantine.
The Independent has contacted Sir William Borlase’s Grammar School for further clarification.
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