Targeted testing is to take place at a school after a case of the new Covid variant Omicron was detected in the county.
Cases were identified in Nottingham and Essex on Saturday.
The UK Health Security Agency (UKHSA) said they were both linked and connected to travel in southern Africa.
Nottinghamshire County Council said investigations into the spread of the variant locally were being carried out at a school in West Bridgford.
Jonathan Gribbin, director of public health for Nottinghamshire, did not name the school but said the parents of students had been informed.
He said testing was being carried out to try to understand how quickly Omicron is spreading across the county and to stop it.
“As part of our investigations into the confirmed case of Omicron in the Nottingham area we are also now working with parents of children at a Nottinghamshire school to seek their consent for some targeted testing and that will be something we will do to get a better understanding of how the variant is spreading,” he said.
Mr Gribbin said the “immediate thing” people could do is get booster jabs as soon as they are eligible and for people to continue testing if they have Covid symptoms.
Both the county council and Nottingham City Council said they were working closely with the UKHSA to identify and trace close contacts of the Nottingham Omicron case.
In a joint statement, the councils said: “There are things we can all do to keep ourselves and others safe.
“Please follow the government instruction to wear a face covering on public transport and in shops and we would strongly advise also in crowded or indoor settings.
“In addition, try to keep your distance from people not in your household.”
A third case of Omicron identified on Sunday came from a visitor who spent time in the Westminster area of London, although the person is no longer in the UK, the Health Security Agency said.
Six cases have also been identified in Scotland.
From Tuesday, mask wearing in shops and on public transport will be mandatory again and rules have returned on PCR testing for people entering the country from abroad.