Last year, only 43% of those eligible for the free flu vaccine in the Hywel Dda health board area had it.
It is hoped a new campaign which highlights the danger of flu for older people will help increase uptake of the vaccination in young children.
“Children are really good at sharing their germs,” said Ros Jervis, the health board’s public health director.
The campaign to vaccinate two and three-year-olds also clarifies that the vaccine is administered nasally.
“It is an illness which can be quite nasty,” said Ms Jervis.
“If those cases are in the over-75s – the really vulnerable, those who would really suffer from flu – then that’s worth doing.”
She said research showed that for every six children vaccinated, one case of flu is prevented.
Ms Jervis said there had been “room for improvement last year” and that the campaign emphasised the method of immunisation – nasal spray rather than a jab – and the benefits to older people
“It is a really simple vaccine which is just squirted up each nostril – it is needle-free, pain-free and very, very simple,” she said.
“Children are really good at sharing their germs. And this is an opportunity to stop it being passed on to more vulnerable people.
“Flu is an unpleasant illness for children as well and there can be some serious complications.”
Ms Jervis said the health board – which covers the Pembrokeshire, Ceredigion and Carmarthenshire areas – was already starting to see the benefits of the campaign, with a 3% increase in children aged two or three years old getting the vaccine.
Rebecca Davies, who manages Dechrau Disglair nursery in Carmarthenshire, said that the way children play encourages the spread of germs.
“They are in close proximity to each other at all times and very interactive, playing with each other, touching, holding hands, developing social skills,” she explained.
She said parents were generally prepared to vaccinate their children if the benefits were made clear.