The category C prison, near Acklington, confirmed that it was taking measures to control the spread of the virus after an unspecified number of staff and prisoners tested positive.
Liz Morgan, Northumberland’s director of public health, revealed details of the outbreak during a council meeting on Thursday morning.
She told the county council’s health and wellbeing board that the authority was “actively supporting management of an outbreak in the prison”.
The cluster of cases at the jail is responsible for giving the Druridge Bay ward by far the highest rate of coronavirus infections in Northumberland.
Latest data shows that 92 positive cases were reported in the ward in the seven days up to February 7 – a rate of 1,410 per 100,000 people.
That is noticeably higher than anywhere else in the county, with the next highest being Morpeth Kirkhill – which recorded 57 cases and a rate of 1,084 per 100,000.
The overall rate of cases in Northumberland is 655 per 100,000, having dropped substantially over the past month since a peak of Omicron cases in early January.
A HMP Northumberland spokesperson said: “A number of staff and prisoners recently tested positive for Covid-19 at HMP Northumberland.
“Measures are in place to ensure the safety of everyone living and working at the prison, including appropriate self- isolation and testing – these are consistent with successful measures we have taken previously.
“We continue to liaise with UK Health Security Agency and the local authority to limit infection transmission.”
Two wings of the prison were locked down during a previous Covid outbreak in October 2020.
That came after an inspector’s report found that some prisoners at the Sodexo-run jail who showed symptoms of coronavirus were locked in their cells for up to eight days, without access to a shower or the open air, until their test result came back.
HM Inspectorate of Prisons also reported that one prisoner with mobility issues had not showered for six months due to coronavirus restrictions that meant he could not get to an accessible bathroom.