More than a third of the people eligible for free flu vaccines in Calderdale did not take them up last winter, figures show.
England’s top doctors are urging people to protect themselves and their families from flu amid warnings that new cases may peak over the busy Christmas period.
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NHS England data shows that 72,983 people were eligible for free flu vaccines in Calderdale last winter – but only 62% of them had one.
The low rate meant 27,483 vulnerable people were left unprotected in the area through the key winter months.
While the flu virus can be unpleasant for anyone, if sufferers are otherwise healthy it usually clears up without treatment within a week.
However, for certain groups of people, such as the elderly, the very young, pregnant women and people with other health conditions, it can be serious and even cause death.
The NHS offers free flu vaccines to all these groups due to their increased vulnerability.
The figures show that toddlers were much less likely to have had the jab than their older neighbours in Calderdale, with parents taking only 40% of two year olds and 45% of children aged three for the vaccinations.
The uptake rate among Calderdale's senior residents was better – but at 72%, around 11,000 over 65s still went without.
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Just 55% of pregnant women received the vaccine, and 52% of under 65s with health conditions which put them at heightened risk.
As flu levels ramp up this year, Public Health England has introduced its Catch It, Bin It, Kill It campaign, to help prevent the spread of the highly infectious disease during Christmas, Hanukkah and New Year celebrations.
It says hundreds of thousands could see their holiday plans turned to misery if flu levels rise as expected in late December and early January.
Professor Stephen Powis, the NHS's national medical director, said: “Whether it’s missing out on your Christmas dinner, the Boxing Day match or a New Year’s party, nobody wants to be laid low by flu while the festivities are in full swing.
“It’s good to see that more people over the age of 65 have already got their jab. For older people and those with underlying health conditions, getting flu is particularly bad news because it can lead to really serious conditions like pneumonia and bronchitis, which can mean a lengthy stay in hospital.
“And we know that children are ‘super spreaders’ of flu, particularly around the holiday season when they’re more likely to see elderly relatives.
“So our message is simple: the flu season is here, get your jab now. It might be the difference between a Christmas to remember, and one to forget.”