Almost 200 prison staff are off due to the coronavirus outbreak, a senior official in Northern Ireland said.
Nearly a quarter of the workforce is absent due to precautions around the infection and unrelated sickness.
There have been no confirmed cases, Northern Ireland Prison Service director general Ronnie Armour said.
A small number of prisoners were being held in isolation and special measures are being taken to protect elderly or otherwise vulnerable inmates.
Mr Armour said: “There is no rule or guidebook to point us to the right answers.”
He said they were attempting to act with certainty but planning for the unknown.
A total of 197 staff are off due to Covid-19.
Another 94 are absent for unrelated sickness, totalling 23% of the current workforce, the senior official told Stormont’s justice committee.
Northern Ireland holds paramilitary and life-sentenced prisoners at its high-security jail at Maghaberry, Co Antrim, as well as significant numbers of increasingly elderly sex offenders at Magilligan on the north coast.
Some sentenced prisoners have been temporarily released due to the highly contagious infection, which could prove devastating in the close confines of a prison.
None are deemed to pose a risk.
A third of the overall population has mental health issues.
Mr Armour said reduced numbers helped social distancing and cut the total sharing cells.
The official added: “Crucially it also means when the more difficult days come we have fewer people to monitor and fewer people to manage.”
At present, managers are “confident” they can cope and the organisation had attempted to maintain as normal a regime as possible.
Visits, temporary release and working in the community ended last month.
The service lodged a sizeable order for personal protective equipment in February including a quarter of a million face masks as well as disposable suits and visors.
The temporary early release of up to 200 prisoners has been announced by Northern Ireland justice minister Naomi Long.
Those serving a life sentence, detained under the mental health act, imprisoned for a terrorist offence and all posing a risk are ineligible for early release.