The attack took place at Altnagelvin Hospital.
Daily Coronavirus cases in Derry City and Strabane have dropped to 64 in the past 24 hours bringing the overall total to 5,156.
Thirteen more Covid-related deaths have been announced in Northern Ireland.
In Derry City and Strabane 41 people have died of Covid-19 since the start of the pandemic, according to Department of Health (DoH) statistics.
The council area has the second highest rate of infection in the country behind Mid Ulster.
Over the past seven days 737 new cases have been recorded locally.
Just two council areas have more cases over the same period, Belfast (1,616) and Mid Ulster (792).
Altnagelvin Hospital has 67 Covid inpatients and the DoH dashboard says that all nine Intensive Care Unit (ICU) beds are now occupied at the Derry Hospital.
However, the Western Trust has told the Derry News that Altnagelvin has capacity for up to 18 ICU beds.
The Derry hospital is now moving into low critical care surge at nine ICU patients.
A spokesperson added: "As numbers increase we increase capacity as per our critical care surge plan up to 18 beds.
"It is important to note critical care beds are managed by CCaNNi - the critical care network."
The Western Trust's resilience plan to address Winter Pressures and waves of the pandemic adds: "Plans in place for medium, high and extreme surge with up to 18 ICU beds in Altnagelvin and 10 at South West Acute in line with CCaNNI recommendations.
"This is reliant on redeployment of staffing from other front line areas in the event of a significant surge that requires this level of critical care beds."
Meanwhile, a DoH spokesperson said the dashboard refers to available ICU beds as things stand today.
“The CCANNI Critical Care Surge Plan allows us to ramp up capacity to a total of 158 ICU beds, if required, through a combination of additional capacity in each Trust and regionally through the Nightingale facility at Belfast City Hospital.
“It should be emphasised that expanding ICU capacity will have knock-on effects on other aspects of the health service - staff will need to be redeployed from elsewhere in the system to support additional ICU beds.
“That is why the CCANNI surge plan incrementally flexes up ICU beds as demand grows,” he added.
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