Health chiefs are urging parents in Brighton and Hove to have their children vaccinated against flu.
They said that younger children are eligible for the vaccine in the form of a nasal spray rather than the traditional injection.
And while some children can have their vaccination at school, younger children should be taken to their family doctor.
A spokesman for the NHS said: “Children aged two, three and four, or in school years one, two and three, are all eligible for the flu vaccination on the NHS.
“The child-friendly nasal spray means children can avoid having an injection and instead have a quick, painless, squirt into each nostril.
“Children aged two to four years old can visit their GP (general practitioner) for the nasal spray vaccination while school nurses are running clinics for children in years one, two and three.
“Children of all ages with a health condition that puts them at greater risk of flu are also eligible for the flu vaccine.
“Flu can be a very unpleasant illness in children causing fever, stuffy nose, dry cough, sore throat, aching muscles and joints and extreme tiredness. This can often last several days.
“Some children can get a very high fever, sometimes without the usual flu symptoms, and may need to go to hospital for treatment.
“Serious complications of flu include a painful ear infection, acute bronchitis and pneumonia.”
Max Kammerling, head of the Public Health Screening and Immunisation Team for Surrey and Sussex, said: “It is important we protect young children from the flu virus in time for winter and get them vaccinated now.
“Children can become very poorly if they catch flu and it impacts on the wider family as parents/carers may have to take time of work to look after them.”
Dr Kammerling added: “The nasal spray contains viruses that have been weakened to prevent them from causing flu but will help children to build up immunity.”
The NHS spokesman said: “It is important to get children vaccinated even if they had the flu vaccination last year.
“The flu vaccine provides protection against the strains of flu that are likely to circulate this year and which may be different from last year.
“So make sure you visit your GP when offered the nasal spray vaccine – for pre-school children – or complete the consent form so your child can have the vaccine at school – for four to seven-year-olds.”
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