Infection rates are higher than average at this time of year for children aged five to 14 years old, and young people aged 15 to 24.

Hospital admission rates are low but are expected to increase over the coming weeks. The dominant strain is Influenza A, which is linked to more severe illnesses and higher morbidity among older people.

The public are advised that vaccination is the best way to protect against the disease, with children, young people under 25, the elderly, pregnant women and other people living with long-term health conditions encouraged to get a free flu jab.

Appointments for free flu jabs can be booked with GP practices, on the NHS app, or by calling 119 (with translators available). Alternatively, search 'NHS pharmacy vaccine' online.

Other members of the public who are not in the most vulnerable groups can also pay for a flu jab at their local pharmacy.

Sarah Perman, the director of public health at Hertfordshire County Council, delivered a presentation outlining the statistics.

She said: "Across Hertfordshire, hospital admissions are still low, but we are expecting those to increase in the next few weeks, in line with those higher case rates.

"That's because we are seeing the dominant virus being a strain of Influenza A, which is associated with more severe illness and higher mortality, particularly in older people, than some of the other viruses we see commonly circulating during the flu season."

The public is advised that although cases are low in Hertfordshire, experts nationally predict the worst flu season seen for many years. Internationally, attention is focused on Australia, which had the worst flu season on record.

It takes around two weeks for the vaccine to take effect, so those who are among vulnerable groups are advised to act quickly in order to be protected when infection rates worsen.

Of the four types of influenza – A, B, C and D – it is strains A and B which are most commonly seen in outbreaks during winter. Strains of flu include fever, chills, headaches, aches and pains in the joints and muscles, and extreme tiredness.

Healthy individuals usually recover in two to seven days, but some people who are immunocompromised may need hospital treatment. Last year, flu caused 80,000 deaths in England, while vaccination prevented 96,000 to 120,000 hospitalisations.

The flu virus is spread when people cough or sneeze, and infection rates speed up in winter when people spend more time together indoors.

Those eligible for a flu vaccine include:

People with long-term health conditions aged six to 65

People aged 65 and over

Pregnant women

All children aged two to three years old on August 31

Primary school-aged children (from Reception to Year 6)

Secondary school-aged children (from Year 7 to Year 11)

Carers and frontline health and social workers

The public is advised that the injectable vaccine given to adults does not contain porcine (pork) derived products, while the nasal spray given to children does contain porcine products. Parents can choose to give their children the adult (non-porcine) vaccine for religious reasons.

Cllr Ajanta Hilton, portfolio holder for public health, said: "We're very aware that some communities do have that vaccine hesitancy and are still looking for more reassurance, so we're really trying to reach our faith communities, through the voluntary sectors, who've got really strong links.

"To their leaders, we're saying 'Please, do push this message across' because whatever hesitancy you do have, the consequences could be much worse."