Flu jabs are vaccines that protect against infection by the influenza virus, and are administered via an injection.

However, the NHS has this week expressed concern that the jab won’t protect the elderly.

Sir Malcolm Grant, chairman of NHS England, has revealed that the health service is “more scared than we have ever been" and have predicted they will be “inundated” as the Aussie flu makes its way to the UK.

His comments at a conference in Bournemouth came as Professor Dame Sally Davies, who as the country’s Chief Medical Officer is England’s most senior doctor, said she feared the jab would not protect the elderly, and urged the 21 million people who are eligible for free vaccinations to take up the offer. These include at risk groups such as children, those with chronic diseases, health workers and the elderly.

The jab is said to be the best protection against flu symptoms that can include a sore throat, joint pain, chesty cough, headache, sudden fever, chills and tiredness.

While many healthy people will recover from the common winter illness within a week, some people may need to be hospitalised.

More worryingly, in Australia -where there has been the worst flu season for 50 years - dozens have died. While it’s important to be vaccinated, the flu does come with certain side-effects.

According to the NHS, these include a mild fever and slight muscle aches for a couple of days.

They recommend if you have a sore arm to move it regularly and to take a painkiller, such as paracetamol or ibuprofen. If you continue to experience side effects that don’t improve over time you should see your GP as soon as possible.

Some people may experience a severe allergic reaction to the flu jab - known as anaphylaxis - but cases are very rare.

Symptoms include feeling lightheaded or faint, having breathing difficulties, wheezing, a fast heartbeat, clammy skin, confusion and anxiety, and collapsing or losing consciousness.

With prompt treatment, individuals should make a quick and complete recovery according to the NHS.