West Park Primary School in Porthcawl, South Wales have told 267 pupils to self-isolate after 26 people tested positive.
Online learning has now been arranged for any pupil who is affected and parents and carers “have been advised to remain alert,” Bridgend County Borough Council spokesman said.
The spokesman added that four staff members and 22 pupils are positive and all the “staff and most pupils” in year 1 have been affected.
The Welsh chief medical officer, Dr Frank Atherton warned that people “should be worried” over the Indian variant of coronavirus cases rising.
Dr Atherton told a daily briefing on Monday they have seen an increase to “around 57″ cases of the new Indian variant whsoich is “something we need to watch very carefully”.
The total last Thursday was 28.
Dr Atherton said that last Thursday there was only 28 cases, and most cases of the Indian variant are in Cardiff and the Vale of Glamorgan.
The chief medical officer told journalists, “We should continue on the cautious approach here in Wales.
“The public should be worried about the resurgence in coronavirus in general really.
“We have a small number of cases, 57 at the moment of the so-called Indian variant, but that will be an underestimate and I expect the numbers to rise.”