Covid cases have been reported at HMP Littlehey prompting officials to “closely monitor the situation”.
Prisoners at the site near Huntingdon were believed to have contracted the virus earlier this week.
The Prison Service said safe prison regimes were operating and additional support had been brought in to assist staff.
A spokesperson said: “Our priority is to limit the spread of the virus and protect the lives of those who live and work in our prisons.
“We have taken precautionary measures at Littlehey, in line with public health guidance, and will continue to closely monitor the situation.”
In March last year an elderly inmate at Littlehey was the first inmate in Britain to die after contracting the virus.
The 84-year-old was said to have underlying health problems.
The site has around 1,200 prisoners, with 12 per cent of the population aged 70 or over.
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