Chemists are calling for people to get a flu vaccine on the eve of the final day to get full protection in time for Christmas.

The flu jab takes up to 14 days to become active - meaning Friday, December 12 is the last possible day a patient can get the jab if they hope to be fully covered for Christmas Day. Pharmacists insist vaccines are still widely available after reports of some High Street chemists running out.

A new aggressive strain called H3N2 - dubbed ‘superflu’ is causing more severe illness even in otherwise healthy people and the infection surge is currently being driven by children.

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Pharmacist George Sandhu, deputy superintendent at the Well Pharmacy chain, said: “The flu vaccine takes up to two weeks to become fully effective and offer maximum protection for patients. A vaccine appointment takes just ten minutes - but it could make the difference between a wonderful or a miserable Christmas. Time is running out.”

Britain is braced for the worst flu season on record with infection rates and hospitalisations well ahead of where they normally are at this time of year. The peak of the flu surge is expected in late December and through January. NHS England will publish latest weekly hospitalisation data today.

Shortages of vaccine appointments or doses have been reported in some areas and pharmacists said people should be prepared to travel or try multiple places, with. Nick Thayer, the head of policy for the Company Chemists Association, which represents large chains such as Boots and Superdrug, told the Telegraph: "There is no national shortage of flu vaccines, but the bulk of them are administered in October and November.

"By the time you get to December some places are running low, and some will have none left from their original allocation. There are a lot of places you can get vaccinated, but you might need to look around a bit - look on the websites for pharmacies, look on the NHS website, if you are eligible for a free jab or talk to your local pharmacy and ask."

Flu vaccines have been available since October for those most at risk of flu complications such as the elderly, pregnant women, young children and those with long-term health conditions. A nasal spray vaccine is available for all children aged two years old up to those in year 11 of school.

For the majority of UK adults aged 17 to 64 there is no free NHS vaccine but it can be purchased privately from chemists for between £17 and £23. The flu vaccine takes up to 14 days to offer maximum protection but from the day after immunisation it starts to provide protection which can crucially reduce flu symptoms if you catch the virus.

Current data indicates three in ten children aged from five to 14 who have taken a test have tested positive for flu after taking a PCR test in England. Chemist Mr Sandhu said parents should follow NHS guidelines and keep their children off school if they have symptoms to stop the spread.

He added: “The flu vaccine takes up to 14 days to fully become effective and offer maximum protection for patients. There is a serious risk this year that many families will be dealing with severe cases of the flu and so I would ask that anyone considering getting vaccinated does so.

“While some patients might still get the flu, it is a much more mild version which lasts for less time than the proper flu would. It is also important to practice good ventilation if meeting people from other households so ensure to open a window every hour for at least ten minutes to allow for fresh air to enter.

“When coughing, do so into a bent elbow to avoid spreading potentially infectious particles across a room especially if you are aware of potentially vulnerable people in the room. Wash your hands frequently with warm water to avoid spreading germs and also ensure to clean frequently touched areas including door handles.”

It comes after NHS leaders warned it’s “now or never” to get kids vaccinated to protect elderly residents from flu over Christmas. Caroline Temmink, the NHS director of vaccinations, said: “As families gear up for festive celebrations together, it's now or never to get protected against flu in time for Christmas.

“Children are super-spreaders and with flu infections rising fast in younger age groups, getting kids vaccinated is one of the best ways to prevent serious illness, especially for grandparents and loved ones who are vulnerable.”