One class at Larchwood Primary School based in Pilgrims Hatch has been moved to remote learning.
The school and Essex County Council said in a joint statement: “We appreciate that this is an unsettling time for parents, pupils and the school community but we take the time to remind everyone that this is a precautionary measure.”
Children very rarely get severely ill from coronavirus but can pass it on to their families.
A number of sites in Essex visited by a person infected with the Omicron variant are being targeted for testing, the county’s director of public health Dr Michael Gogarty told BBC Breakfast, including KFC in Brentwood, a faith setting and a school.
“What we’re doing is we’re throwing the net very wide in terms of requesting people who attended these places at the particular times to get tested as soon as possible,” he explained.
“Within the school we are actually excluding one school group as close contacts, but with the rest of the school group we would wish them to get tested and we are arranging for that testing to happen.
“Some sought it yesterday, and the rest will happen today.”
Health chiefs are racing to trace contacts of people who have been confirmed to have been infected with Omicron which may be more resistant to vaccines and could spread more quickly than the Delta variant which is dominant in the UK.
Six cases have also been identified in Scotland and one in London, in the Westminster borough, and more are expected to be discovered in coming days in parts of the country.
The Essex statement added: “Following further contact tracing of the known Omicron Covid-19 case in Brentwood, it has been confirmed that there is a link to to Larchwood Primary School based in Pilgrims Hatch.
“The UK Health and Security Agency, Department of Health and Social Care, Larchwood Primary School and colleagues from Essex County Council and Brentwood Council have worked together to take necessary precautionary action to prevent the spread. This includes making specialist testing available for all pupils and school staff and confirming arrangements for remote learning for one class.”