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How Does the Flu Vaccine Work?

  • Writer: Dr Joseph Nightingale
    Dr Joseph Nightingale
  • Sep 17
  • 6 min read

Updated: Sep 18

A woman with the flu

The flu vaccine introduces a harmless part of the virus, helping your immune system recognise and fight flu if exposed. By building this protection in advance, it lowers your chances of getting seriously ill and helps limit the spread of flu through the community.


Flu isn’t just a heavy cold. The viral infection spikes during the winter months (known as seasonal flu) and is highly infectious. More severe than a cold, it starts with a runny nose or sore throat and progresses to fever, chills, headaches, pains in the joints and muscles.


Individuals can be bedridden for several days, and for those with prior conditions, the disease can lead to permanent disability or even death.


But how does the flu vaccine work? Is the flu vaccine a live vaccine? How long does it last? And is it safe? Find out below.


Is the Flu Vaccine a Live Vaccine?


In the UK, the flu vaccine is not a live vaccine. It uses inactivated (killed) flu viruses or parts of the virus, meaning you cannot get infected. For most adults, the flu vaccine is safe, including people with long-term conditions or weakened immune systems. 


There is an exception: one type of flu vaccine given to children via nasal spray is live but weakened. The nasal spray flu vaccine is a ‘live attenuated influenza vaccine’ (LAIV), which cannot cause the illness but gives strong protection. It is only available to:


  • Children aged 2–17 years

  • Given at GP surgeries for 2–3 year olds

  • Given in schools for school-aged children

  • Children with long-term conditions (if suitable)


If LAIV isn’t suitable - for example, in children with certain medical conditions, those who are severely immunocompromised, or where there are faith concerns - an inactivated injection is available.


Why Should I Get a Flu Jab Every Year?


The flu vaccine does not provide lifelong protection. Flu viruses are constantly changing, so new strains circulate each winter. Even if you’ve had flu before, or last year’s vaccine, your protection won’t be enough this year.


The flu jab is recommended for everyone, but only certain groups are eligible for a free NHS vaccine:


  • Adults aged 65 and over

  • Children and adults with certain health conditions (including babies over 6 months)

  • Pregnant women

  • Children aged 2–3 years (on 31 August)

  • All primary school children

  • Secondary school children in Years 7–11

  • People in care homes

  • Carers and those receiving carer’s allowance

  • People living with someone who has a weakened immune system

  • Frontline health and social care staff


Flu is more than just a heavy cold. For vulnerable people, it can be dangerous — in the 2022–23 season, flu was linked to around 14,500 deaths. In 2024–25, it caused over 15,000 hospital admissions, with more than 5,400 people in hospital each day at the peak of the season.

Getting vaccinated each year is the safest and most effective way to protect yourself and those around you. Don’t wait until flu season is in full swing. Join the waitlist for your flu jab in Coventry at Health Klinix today - it only takes a few minutes.


Does the Flu Vaccine Work?


Yes, the flu vaccine is highly effective.


It trains your immune system to recognise and fight the flu virus by introducing elements of the virus. 


Your body becomes immune to the pathogen (ie virus) by identifying protein markers on their surface. Usually, it does this during an ongoing infection. Vaccines offer the opportunity to identify the markers without fighting the disease.


The CDC (in the US) tracks how well the flu vaccine works each year. On average, it prevents flu in around 4 in 10 people - and protection is even higher in children, with success rates of up to 65%.


But even if the vaccine doesn’t fully prevent infection, it often reduces how severe your illness is.


How Long Does the Flu Vaccine Last?


The flu vaccine protects you for around six months to a year, which covers the winter flu season. Because immunity fades and flu strains change, a new jab is recommended every year to keep your protection up to date.


Find out more about the types of flu jabs in our Why Are There Different Types of Flu Vaccines article.


Is the Flu Jab Safe?


Yes, the flu jab is extremely safe. Most people get few or no side effects from the flu jab.


Common side effects include:


  • Soreness, redness, or slight bruising where the injection was given

  • A mild fever

  • Achy muscles

  • Headache

  • Feeling sick (nausea)

  • Feeling generally under the weather


These side effects will pass within a few days.


All vaccines in the UK undergo strict testing for safety and effectiveness before being approved - the flu vaccine is no exception. Millions of people receive the flu vaccine safely every year, including pregnant women, children, and older adults.


There is far more risk from flu infection than from the vaccine. For people with long-term conditions or weakened immune systems, the benefits of the vaccine outweigh any risks.


Does the Flu Vaccine Give You the Flu?


No, the flu jab cannot give you the flu.


Most people receive an inactivated vaccine, meaning it cannot infect you. You may still feel a bit achy, tired, or develop a mild fever after vaccination. However, that’s due to your immune system response.


Some children receive the nasal spray vaccine, which contains a weakened live virus. In extremely rare cases, children may develop mild, cold-like symptoms, but this is not the same as influenza. The symptoms will pass within a few days.


Book Your Flu Jab in Coventry


Flu season hits hard every year, especially for older adults, young children, and anyone with a long-term condition. The flu jab is your best protection, and it only takes a few minutes.


If you're in or around Coventry, you can join the waitlist for your flu vaccine directly with Health Klinix. We're here to answer any questions and make the process simple.


Join the flu jab waitlist now - and stay one step ahead this winter.


Flu Vaccine Frequently Asked Questions


How can I stop myself from getting the flu?


The most obvious solution is to get vaccinated.


Otherwise, the advice is similar to that for other infections. During flu season, maintain excellent hygiene, washing your hands frequently and using alcohol gel after touching public surfaces. You might want to minimise your contact with sick individuals.


You can also boost your immune system. Exercising, eating healthily, and getting enough sleep mean you’re ready to fight any infection. Certain foods and supplements like Vitamin D, and possibly Vitamin C and zinc, may reduce the incidence of infection but the evidence is inconclusive.


You can read more about flu prevention in our 5 Expert Tips to Prevent Flu article.


I’m pregnant, can I get the flu vaccine?


Yes, pregnant women can receive the flu jab. 


In fact, it’s recommended that all women receive the annual flu jab due to the risks of infections. Women who develop the flu during pregnancy are associated with a greater risk of prematurity, low birth weight, and other pregnancy problems.


Your midwife or GP can provide the flu vaccination. Alternatively, you can contact Health Klinix to arrange your flu vaccine in Coventry at your earliest convenience.


You can read more about this in our Pregnancy and the Flu Jab article.



Can I get the flu vaccine if I’m ill?


Yes, if you have a mild illness (like a cold, sore throat, or runny nose), you can still have the flu vaccine.


If you’re feeling very unwell with a high fever, you should wait until you’re fully recovered. Your body is still fighting an infection. You want it to react correctly to the vaccine, giving you the best chance of flu immunity. It also helps avoid confusion between your current symptoms and any vaccine side effects.


References:



Written by:


Dr Joseph Nightingale, MBBS, MSc


Approved by:


Dr Ravi Gowda

Consultant Physician in Infectious Diseases

MBBS, MRCP(UK), DTM&H, MRCGP, DCH, DRCOG, DFFP

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