The Health Service Executive has warned that the virulent H1N1 flu strain - also known as swine flu - is in Ireland and could become a potentially serious public health issue.

The HSE's Assistant National Director for Public Health, Dr Kevin Kelleher, said that already a number of people - including those in the 20s, 30s and 40s - have been admitted to hospital intensive care units.

Speaking on RTÉ’s News at One he said at least two, and possibly four, people have died.

Dr Kelleher said that the flu strain circulating can be problematic for people under the age of 65, predominantly those with a pre-existing disease and pregnant women.

He said it can cause chest problems that can bring on pneumonia, which affects breathing.

He said it was not too late to get the flu vaccine and urged vulnerable people in particular to get it.

Dr Kelleher said most people who get the flu should stay at home in bed, but those who feel seriously ill could call their GP or out-of-hours numbers.

"I know it's difficult not to let your child go to school, or not yourself go to work, but it is important if you've got these symptoms," he said.

Dr Kelleher also warned that people with flu symptoms should not visit elderly or vulnerable people.