Young people and pregnant women are among the most vulnerable in this year's flu season, experts have warned.
This is because swine flu, the AH1N1 virus, could be the dominant strain circulating this winter.
The forecast was made at a meeting of the Emergency Department Taskforce.
HSE public health specialist Dr Kevin Kelleher said that if the pattern is the same here this winter as the Australian flu season, it will be swine flu that could dominate.
The age profile of those who fall ill will be younger, and there tends to be a slight increase in pregnant women when this strain predominates, he said.
It will mean more pressure on hospital intensive care units.
However, there are usually lower rates of illness in older people and there tend to be fewer outbreaks than when another A strain of the virus, AH3N2, is more common.
Dr Kelleher cautioned that there could be a pool of susceptible individuals, particularly children under four, who could pass it on to the elderly. He said predicting how the flu season will turn out was difficult.
Swine flu is dominant so far this winter, which could mean the scenario outlined will mark this year's season.
There is currently a low level of flu circulating and a relatively small number of cases. The ratio of swine flu to the B virus is around 60:40.
One of the plus sides of swine flu is that it is better covered by the seasonal flu vaccine.
Flu rates traditionally spiral around the end of December and early January as more people travel and congre- gate in homes and at social gatherings, increasing the risk of spread.
It contributes to the rush of patients attending emergency departments, fuelling the trolley crisis.
Last winter brought a prolonged flu season with a higher percentage of the B strain of virus. The elderly were hospitalised in large numbers and also admitted to intensive care units.
The outbreaks of flu in nursing homes were the highest ever recorded and there were excess deaths for 11 weeks.
Overall, there were 255 notified flu deaths last winter, the highest ever recorded, according to reports.
The median age of those who died was 81.