The Flu Vaccine: Who Needs It, How It Works, and When to Get It

Flu , short for influenza , is far more serious than a common cold. It can put you in bed for a week, lead to complications like pneumonia or bronchitis, and in vulnerable people it can be life-threatening. Each year in the UK, flu-related complications are responsible for thousands of hospitalisations. The 2025/26 season has already been notable, driven by a strain of H3N2 influenza that spread unusually early.

The single most effective thing you can do to protect yourself , and the people around you , is to get the flu vaccine before the season peaks. This guide covers everything you need to know: how the vaccine works, who is eligible for a free NHS jab, who should book privately, when to get it, and what to expect.

Influenza is a highly contagious viral infection that affects the respiratory system. Unlike a cold, which develops gradually, flu typically comes on quickly and severely , with a sudden high fever, aching muscles, exhaustion, a dry cough, and a headache that makes it hard to function.

For most healthy adults, flu means several miserable days at home. But for certain groups , older adults, pregnant women, people with chronic health conditions, and those with weakened immune systems , flu can trigger serious complications including:

•       Pneumonia and severe chest infections

•       Worsening of existing conditions such as asthma, heart disease, or diabetes

•       Hospitalisation , flu leads to tens of thousands of hospital admissions in the UK every year

•       In the worst cases, death , particularly in people aged 65 and over

Flu also spreads very easily. When an infected person coughs or sneezes, the virus travels through the air and can be picked up by people nearby. It can also survive on surfaces and be transmitted by touch. Vaccination protects not only you but also the people around you who may be more vulnerable.

The flu vaccine works by introducing your immune system to proteins found on the surface of flu viruses. Your body learns to recognise these proteins and builds antibodies against them. When you encounter the real flu virus, your immune system is primed to fight it off quickly , reducing your chances of getting ill, and reducing the severity of illness if you do.

There is one crucial detail that surprises many people: the flu vaccine cannot give you flu. The injected vaccines used in the UK for adults contain inactivated (killed) viruses , they cannot cause infection. If you feel a little under the weather in the day or two after your jab, that is your immune system responding to the vaccine, not a sign you have caught flu.

Why do I need it every year?

Flu viruses mutate constantly. The strains circulating this winter may be different from those circulating last winter. Vaccine manufacturers and public health agencies work together each year to identify which strains are most likely to dominate the coming season and update the vaccine accordingly. Last year's jab may offer little or no protection against this year's strains.

Protection from the vaccine also decreases over time. Even if the strains remain similar, your immunity from the previous year's jab may have waned enough to leave you vulnerable. This is why annual vaccination is strongly recommended , not just for at-risk groups, but for anyone who wants reliable protection.

In the UK, the NHS offers a free flu vaccine to people who are most at risk from serious illness. Everyone else can get vaccinated privately. The table below summarises who falls into each category:

If you are unsure whether you qualify for a free NHS flu vaccine, check on the NHS website or speak to our pharmacist. The eligibility criteria are set nationally and updated each season.

Timing matters. Here is a practical guide to when to book:

At Longeva Clinic we offer private flu vaccinations from early autumn. This means you can often be vaccinated ahead of the main NHS rollout, giving you protection in place before flu begins to circulate in your community.

Getting the flu vaccine at Longeva Clinic is a quick, straightforward process. Most appointments take around 10 minutes from start to finish.

•       You will be asked a few short questions about your health history and any allergies before the vaccine is administered , this is a routine safety check

•       The vaccine is given as a single injection into your upper arm

•       You may be asked to wait for a few minutes after the jab , this is standard practice to ensure there is no immediate reaction

•       You will be given aftercare advice before you leave

No referral from a GP is needed. You can book directly online and attend at a time that suits you.

The flu vaccine has an excellent safety record , millions of doses are administered in the UK every year. For the vast majority of people, it is very well tolerated.

Common side effects (mild and short-lived):

•       Soreness, redness, or mild swelling at the injection site , the most common side effect, typically resolving within 24, 48 hours

•       Mild fever or feeling slightly under the weather for a day or two

•       Headache or muscle aches

•       Fatigue

These side effects are a sign that your immune system is responding to the vaccine , they are not a sign that you have caught flu, and they are not a cause for concern. Paracetamol can help if you are uncomfortable.

Rare but serious reactions:

Severe allergic reactions to the flu vaccine are very rare , estimated at fewer than one per million doses. Our pharmacist is trained to recognise and manage an allergic reaction immediately. If you have a history of severe allergic reactions to previous flu vaccines, please let us know before your appointment.

You should delay your vaccination if you are currently unwell with a fever. A mild cold or a slight sniffle is not a reason to postpone , only a fever warrants waiting until you feel better.

"The flu vaccine can give you flu."

False. The injected flu vaccines used for adults in the UK contain inactivated (killed) viruses and cannot cause flu. Any mild symptoms you experience in the day or two after vaccination are a normal immune response, not flu.

"I had flu last year so I am probably immune."

Not necessarily. There are multiple strains of flu circulating at any time. Having one strain does not protect you against others. And the strains circulating this winter may be entirely different from those you were exposed to previously. The only reliable annual protection is vaccination.

"It is too late in the season to bother."

Rarely true. Flu typically circulates from November through to March or April. A vaccine administered in January or February still offers meaningful protection for the remainder of the season. Late vaccination is almost always better than no vaccination.

"I am young and healthy so I do not need it."

Healthy people can still catch flu and feel severely unwell for days. They can also transmit it to people around them who are more vulnerable. Vaccination protects you and contributes to reducing the spread of flu in your community.

Can I have the flu vaccine and another vaccine at the same time?

Yes. In most cases, the flu vaccine can be administered alongside other vaccines, including Covid-19 boosters. Our pharmacist will confirm whether this is appropriate for you at your appointment.

I am pregnant. Can I have the flu vaccine?

Yes , and you should. Pregnant women are eligible for a free NHS flu vaccine at any stage of pregnancy. Flu during pregnancy can be particularly serious, and vaccination protects both you and your baby. The flu vaccine has been given safely to pregnant women for many years.

How long does the flu vaccine take to become effective?

It takes approximately 10 to 14 days after vaccination for your immune system to build full protection. This is why early autumn is the ideal time to get vaccinated , before flu is actively circulating in your area.

Can children have the flu vaccine?

Yes. Children aged 2 to 3 are offered the flu vaccine as a nasal spray through the NHS. School-age children typically receive the nasal spray through their school. Children in clinical risk groups are eligible for the NHS vaccine from 6 months of age. Speak to your GP or practice nurse about your child's eligibility.

What if I have an egg allergy?

The standard flu vaccine is grown in eggs and may contain a small amount of egg protein. Most people with egg allergy can still receive the standard vaccine safely. If you have had a severe allergic reaction to eggs in the past, please mention this when booking , we will advise on the most appropriate vaccine for you.

How much does the private flu vaccine cost at Longeva Clinic?

The private flu vaccination at Longeva Clinic costs £15. No GP referral is needed. Book directly online and attend at a time that suits you.

Longeva Clinic offers private flu vaccinations with same-week appointments, no long waits, and clinical advice from our GPhC-registered pharmacist. Whether you are not eligible for the NHS jab or simply want flexibility over when and where you are vaccinated, we make it simple.

Longeva Clinic  ·  Unit 1 Chichester Court, Milnrow Road, Rochdale, OL16 1UG  ·  hello@longevaclinic.co.uk

CLINICAL DISCLAIMER

This article is written for general informational purposes and does not constitute medical advice. NHS flu vaccine eligibility criteria are set nationally and may change each season , always check NHS.uk or speak to a qualified healthcare professional to confirm your eligibility. Longeva Clinic is registered with the GPhC (registration number 2241860).