Beaumont Hospital is yet to fill some 235 staff positions - with the hospital operating with a shortage of 116 permanent nurses, according to new figures seen by the Herald.
The hospital has seen the number of permanent nursing vacancies almost double in the past three months.
It is believed 62 nursing positions were unfilled at the North Dublin hospital in October - with a total of 143 staff positions left vacant.
Since October, the hospital has recruited 30 nursing students, dropping the present nursing shortage to 86.
Lorraine Monaghan, of the Irish Nurses and Midwives Organisation (INMO), told the Herald that the "severe shortage" in nurses is down to a very high attrition rate at the hospital.
Ms Monaghan said that, while hospital management have been actively recruiting staff, a high number have been leaving the hospital for a number of different reasons.
She said that location and working conditions were two of those reasons.
"Obviously, there are major issues when staffing levels are so low, because patient care is compromised and staff are faced with intolerable workloads - and there's an impact on their own health and well-being, so there's an impact for staff as well," she said.
"Staff feel obliged to work additional shifts to help out their colleagues and it's unsafe - they're working more and it's putting them under extreme pressure," she added.
Ms Monaghan said "a lot of work needs to be done to bring nurses back home", adding: "These nurses left the country to get jobs and superior working conditions. They're desperately needed in this country and you can see that in the likes of Beaumont - they are recruiting but are struggling to get nurses to fill the positions," she added.
Meanwhile, the hospital worst hit by overcrowding yesterday said "every available bed space" had to be brought into service as more than 50 patients endured long waits on trolleys in its emergency department.
The spokesman for St Vincent's Hospital in Dublin said it had also cancelled all non-urgent procedures for the next 24 hours due to the surge in patients. Nationally, the numbers on trolleys breached the 500 mark again yesterday morning.
Health Minister Leo Varadkar, who briefed the Cabinet on the ongoing trolley crisis, said it will be another two weeks before the levels of flu peak.
The virus is now a major driver behind emergency department congestion, with the numbers of patients with it presenting for treatment up 10pc, he added.
The Cabinet was told that 'at risk' groups are being urged to get the flu vaccine .
Other measures include using private hospitals to cater for patients on public waiting lists, offering more staff overtime and increasing community intervention teams.