PREGNANT women are now being advised to get seasonal flu vaccines even if they have been immunised against swine flu.
The HSE wrote to GPs advising of the change in the national influenza vaccine policy.
The move comes after a meeting of the National Immunisation Advisory Committee (NIAC) on Monday.
Dr Kevin Kelleher, assistant national director of population health at the HSE, said that it was due to the serious symptoms which affect pregnant women in particular.
"There is evidence that influenza B can cause significant morbidity for pregnant women," he said.
The advice is that all pregnant women who were relying on past immunisation should return to their doctor.
"Even those women who have received only pandemic vaccine previously remain at risk for influenza during the current influenza season," Dr Kelleher said. "Seasonal flu vaccine will offer protection against both the H1N1 and influenza B strains."
The NIAC said that the seasonal flu vaccine can be given at any stage of pregnancy.
However, they have advised that there must be a minimum gap of three weeks since a woman received a swine flu shot before the seasonal vaccine could be administered.
Brian Marsh, consultant in intensive care medicine in the Mater Hospital said that the seasonal flu this year is effectively the H1N1 that was experienced in 2009.
"It's causing very serious problems in younger adults in particular," he said.
But he could not say whether the numbers have reached a peak. "It's a bit early to say at this stage but the evidence is that we have plateaued," he said.
Although experts correctly predicted that influenza A (H1N1) 2009 would be the main virus contributing to this winter's epidemic, the level of influenza B infection was unexpected.
The World Health Organisation has included a strain of influenza B in this year's seasonal vaccine, which matches the virus now in circulation.
Dr Mel Bates of the Irish College of General Practitioners said the HSE "did not appreciate the level of anxiety GPs see around influenza vaccination across the entire population".
But he said that family doctors should have adequate supplies of seasonal flu vaccine to immunise at-risk groups.