Health officials are carrying out coronavirus testing at three more schools in the Greater Glasgow and Clyde area.
Test and Protect teams are contacting pupils and staff who may have come into contact with the virus, it was announced on Friday.
The health board confirmed they are probing possible cases at Castlehead High School in Paisley.
Efforts are also ongoing to trace people connected to Knightswood Primary and St Andrew’s Secondary, both in Glasgow, who may have been exposed to the killer bug.
Public Health teams have established a list of close contacts and are telling them to self-isolate.
A spokesperson for NHS Greater Glasgow and Clyde said: “At this time there is no evidence of transmission within the schools themselves.
“Public Health, education departments and council environmental health teams are working together to support schools and families affected
“Within each of the schools, Public Health teams have systematically established a list of close contacts.
“Test and Protect staff are contacting those identified as contacts.
“These close contacts are being advised to self-isolate and being given appropriate advice and support.
“Robust control measures are in place within each of the schools. Apart from those who are identified as close contacts, all other pupils and staff can continue to attend as normal.”
They added: “We ask the public to remain vigilant.
“The general measures to minimise the risk of COVID-19 remain the same – social distancing, regular hand washing, and being on the look-out for symptoms.
“Anyone with symptoms should immediately self-isolate and seek a test.”