Medical experts warned swine flu will be the worst strain of the virus this winter as the seasonal vaccination campaign begins.
The Health Service Executive (HSE) has urged at-risk groups such as mothers-to-be and older people to get the single injection to protect against three types of the illness.
Brenda Corcoran, of the HSE national immunisation office said: "The flu vaccine cannot give you the flu as it does not contain any live flu virus.
"We want to ensure that people in the at-risk groups, and pregnant women, get the annual flu vaccine this year so that our most vulnerable groups are kept safe this winter from the three most common strains of flu, which this year includes swine flu."
One jab will protect against swine flu, which was infecting 7,000 people a week this time last year, and two other types of the virus.
The HSE said at-risk groups include everyone over the age of 65, pregnant women, health care workers and children and adults with long-term illnesses like asthma and heart conditions.
The injection is free but patients without a medical card or GP visit card will have to pay for their doctor to vaccinate them.
Experts also said healthy pregnant women and mothers who gave birth in the last six weeks and have not previously received the swine flu vaccine should get the seasonal vaccination this year as they are at a higher risk of complications from swine flu.
They said pregnant women who have a long-term medical condition such as diabetes, heart or lung disease need to get the seasonal vaccine even if they have already had the swine flu jab.
The HSE said there are no safety concerns with the seasonal flu vaccine for those who have previously received the swine flu vaccine.