At-risk groups are being urged to get the flu vaccine, as influenza rates rose during the second week of January.
Despite some concerns being expressed at the overall effectiveness of the current flu vaccine, medical advice indicates that it may shorten the duration of flu.
The vaccine is for a different strain of flu than is currently circulating, and is believed to only be about 25% effective.
Emergency medicine consultant at Sligo General Hospital Fergal Hickey said people at risk are still better off being vaccinated.
Speaking on RTÉ's Morning Ireland, Dr Hickey said they advise people over 65 and people with chronic medical conditions to get the vaccine on the basis they are deemed to be high risk.
He said: "The reality is these are the patients who are waiting on trolleys in emergency departments for hospital admission, so that's an opportunity for influenza.
"If somebody arrives to an emergency department with influenza into a very overcrowded environment, [it is an opportunity] for this to spread to other vulnerable patients".
There is an increased risk when these vulnerable people are together in very confined spaces without the appropriate vaccine protection, he said.
He also said that flu kills people every year in Ireland.
Speaking on the same programme, Director of the Health Protection Surveillance Centre Dr Darina O'Flanagan said vulnerable groups should get the vaccine.
She said the flu causes on average 300-500 deaths a year, and up to 1,000 in a bad year, adding "25% of a thousand deaths is a really important preventive measure".
She urged people in at-risk groups, people who have chronic health conditions, those with weakened immune systems, older people, pregnant women, people who are very overweight, health care workers and people who are caring for those in at-risk groups, to make sure they have the vaccine.
Number of people on trolleys in hospitals falls
The number of patients in Emergency Departments or on wards waiting for admission to a bed has reduced further today to 290.
The hospital most affected today is Our Lady of Lourdes in Drogheda with 30 patients waiting.
Other hospitals with significant overcrowding include Connolly Hospital in Dublin with 25 patients and the Mater Hospital with 23.
Meanwhile, the Irish Medical Organisation has said that Minister for Health, Leo Varadkar is wrong to dismiss the role of resources in the overcrowding crisis.
Its president, Dr Trevor Duffy said that cutbacks were at the heart of the current problems, given that the number of acute hospital beds fell by 13% between 2007 and 2013.
He also said that home help hours and long stay beds had been reduced.
