More than 200,000 people across Sussex are at risk of developing serious complications if they catch flu this winter.
They are all eligible for a free flu jab but have not taken up the offer.
Pregnant women are most at risk with just over a quarter taking advantage of the vaccine.
Clincs have been set up at GP practices across the county since September in a bid to get as many people protected as possible before the flu season hits.
Other eligible groups include people over 65, those with long term health conditions such as diabetes, asthma, heart disease and multiple sclerosis and carers.
The latest figures for Sussex show pensioners are the group most likely to have the vaccine, with 57.6% coming forward.
However just 34.3% of those with long term health problems and 27% of pregnant women have had the jab.
Julia Dutchman-Bailey, chief nurse at NHS Sussex, said: “People should not underestimate the dangers of seasonal flu.
“Even a mild flu season can contribute to more than 2,000 deaths each winter across the country – the majority of which could be prevented if those people had been vaccinated against the seasonal flu virus.
“Flu is a highly infectious illness and people with who are already vulnerable can become seriously ill and may require hospital treatment if they catch it.
“These are only early figures in terms of the uptake and we hope that they increase significantly over the next few weeks.
“We want to encourage everyone who is eligible to take this seriously and look after their own health and protect themselves and those around them.
"The jab is available for free at your GP surgery and I would strongly advise anyone who has not yet had the jab to contact their practice to make an appointment as soon as possible."
From the latest figures the number of people over the age of 65 and those with long term conditions receiving the vaccination is lower that at the same point in the campaign last year.
However the number of pregnant women having a free flu jab is slightly higher.
Pregnant women who catch flu are at increased risk of serious complications such as bronchitis and pneumonia.
For more details, visit www.nhs.uk
See the latest news headlines from The Argus:
- Widow’s anguish after grave is vandalised
- Boy joins women-only race for cancer charity
- Second car in police chase hit and run
- Protesters disrupt open day over staff “demotions”
- Killer had taste for blood before terror attack