Around 50 inmates are believed to have contracted the virus at the jail near Wolverhampton, with bosses trying to contain the spread.
Prisoners have been put into almost complete lockdown to try and bring the situation under control at the jail which has around 700 inmates.
Recent outbreaks at Featherstone and nearby Oakwood Prison have played a significant part in Staffordshire's sharp rise in Covid cases. Getting them under control could be key to determining what restrictions are imposed when England comes out of lockdown next month.
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A Featherstone prison officer, who is currently self-isolating because of the outbreak, said there were around 50 cases in total and 30 on one wing alone.
He said: "About two weeks ago four staff tested positive. Then there was a sudden jump to 32.
"It has gone into lockdown, with restrictions on movement. They are still getting exercise but not as much as they were. They are trying to limit the spread."
Prisoners have spent much of the year inside their cells for around 22 hours a day due to the threat of coronavirus, leading to concerns about their health.
A Prison Service spokesman said: “Our priority is to limit the spread of the virus and to protect the lives of those who live and work in our prisons.
“We have taken precautionary measures at HMP Featherstone following a number of positive cases, in line with public health guidance, and will continue to closely monitor the situation.”
Prison governors have faced a constant battle to keep Covid out of cells, with the nature of jails meaning the virus had been able to spread rapidly.
Campaigners have criticised measures which have effectively seen prisoners spend most of their time in solitary confinement.