The Health Service Executive is urging people in at-risk groups to get vaccinated against influenza as figures suggest uptake last year was well below World Health Organization targets.
Research shows that flu can cause up to 1,000 deaths in Ireland during a severe season and that it is easily spread.
The executive is urging those in at-risk groups to get the vaccine as soon as possible.
This includes everyone over the age of 65, anyone suffering from a chronic illness, pregnant women, residents of nursing homes and healthcare workers.
Anyone with flu symptoms, which include a high temperature, sore muscles, headache, cough and sore throat, is urged to stay at home.
The vaccine and consultation are free for those with a medical card or GP visit card.
The HSE said indications so far suggest the national uptake rate for the 2015/2016 season was lower than previous seasons.
55.4% of people aged 65 and over who hold a medical card or GP visit card received the vaccine, which is well below the WHO target of 75%, the HSE added.
"The flu vaccine is the only defence against flu, yet every year many people in the at-risk groups fail to get vaccinated and so put themselves at risk of serious illness or even death," said Dr Brenda Corcoran, Head of the HSE's National Immunisation Office.
"The vaccine reduces infection and associated illnesses and hospitalisation.
"Flu is very infectious and can cause potentially serious illnesses especially for older people, those who have a chronic illness, those with weakened immune systems and pregnant women.
"Seasonal flu vaccine can be given at any stage of pregnancy and also protects the baby.
"The flu vaccine cannot give you the flu as it does not contain any live flu virus and all those at risk should get vaccinated as soon as possible this year to make sure that they are protected," she added.