The flu jab given to thousands of people in Ireland this winter provided poor protection against one of the main killer strains, a new study reveals.
The vaccine was least effective against the A(H3N2) strain - known as 'Aussie flu' - which was responsible for around four in 10 deaths from the virus.
It was just 8pc effective against this strain among people of all ages, the findings from a study of the jab in nine European countries, including Ireland, revealed.
The vaccine provided "moderate" protection against the other major strain circulating, influenza B.
The interim findings showed the response rate from patients to the jab varied between 39pc to 52pc against the B strain.
It was most effective against swine flu (H1N1) but there is little of this circulating this year.
This winter has seen one of the most prolonged flu seasons in years, with 116 deaths from the virus and 3,281 patients hospitalised due to complications.
There were 24 flu outbreaks in hospitals as they battled with overcrowding due to the trolley crisis.
The most recent report shows flu is on the wane in Ireland, although it is still circulating.
The closure of schools and workplaces last week may have helped reduce the spread of infection. However, the colder temperatures may also have the effect of prolonging the survival of the virus while the necessity for more people to be confined indoors at close quarters could mean it may be more easily passed on.
The study on the flu jab, which was led by French epidemiologist Dr Marc Rondy, concluded the conventional vaccine is least effective among the over 65s, who are hardest hit by the virus.
It points to the recommendation in the UK to give older age groups a different winter jab known as adjuvanted trivalent inactivated vaccines.
Adjuvants work to boost our immune response to a vaccine and make it more effective and long-lasting.
Dr Cillian de Gascun, director of the National Virus Reference Laboratory in UCD, pointed out that the World Health Organisation, which decides on the ingredients for the flu vaccine each winter, has recommended a change in the H3N2 component for next season.
He said this new component is included in the flu vaccine for Australia. "So we'll be keeping a close eye on their season, and hoping to see improved vaccine effectiveness rates," he added.