The Health Service Executive has ordered an extra 100,000 seasonal flu vaccines.
The drugs will be used to maintain a continuity of supply against swine flu if infection rates keep rising, as they are expected to do.
Elderly people and those in risk groups have been advised to arrange for vaccinations as soon as possible.
Fine Gael Health Spokesman Dr James Reilly has said there is a great risk of swine flu spreading in hospitals because of overcrowded emergency departments.
Dr Reilly said the overcrowding was putting seriously ill patients at enormous risk of cross-infection from swine flu and other contagious diseases.
He said: 'Acutely ill patients who have been left waiting in overcrowded emergency departments are at enormous risk of contracting swine flu, posing serious risk to their lives.
'An unprecedented number of people are being left for days on trolleys and plastic chairs, in overcrowded emergency departments, waiting for admission to hospital.
'Specifically, patients whose immune systems have been compromised because of cancer treatments, or who have cystic fibrosis, are being left sitting on chairs in overcrowded conditions, for prolonged periods, in close proximity to patients with swine flu.'
Meanwhile, the Department of Education has issued advice to schools on containing the virus as students prepare to return to school on Monday.
The Department has urged school authorities to encourage hand washing, to promote the use and proper disposal of tissues for coughing and sneezing and to familiarise themselves with the symptoms of swine flu.
There have been no deaths from the virus in the Republic of Ireland, but 13 people have died from the virus in Northern Ireland since November.
Nine of those 13 people had underlying health conditions.
Those with lower immunity due to disease or treatment, such as steroids or cancer therapy, are also advised to be vaccinated.