Guidance

Influenza (Flu) vaccine factsheet – Information for patients, parents and carers

Published 1 September 2026

1. Overview of flu

• Flu is a respiratory infection caused by influenza viruses and while it primarily affects the nose, throat, and lungs, flu also causes symptoms throughout the entire body
• Flu can spread easily through tiny droplets when someone coughs, sneezes, or talks, or by touching a contaminated surface
• Symptoms can often begin suddenly and may include fever, tiredness, aches and pains, and difficulty breathing
• While many people recover quickly, flu can sometimes cause complications such as pneumonia or worsening of existing health conditions
• Young children, older adults, pregnant individuals, and people with weakened immune systems are more likely to become seriously unwell from flu infections
• Unlike some viruses, the influenza virus constantly changes over time. Updated vaccines are needed every year to ensure protection against the flu virus strains that are currently circulating

2. Flu vaccination and eligibility

• The flu vaccine is offered on the NHS every year in autumn or early winter to people who are at higher risk of becoming seriously unwell from flu, such as infants, children, older adults, pregnant individuals, and people with certain long-term health conditions
• Local eligibility and vaccination arrangements may vary, and not everyone will be offered the same type of flu vaccine. For more information about eligibility, please see NHS flu vaccine guidance
• If you are not eligible for a flu vaccine through the NHS, you can still be vaccinated in a private clinic
• Your healthcare professional can advise whether the flu vaccine is recommended for you or your child
• If you are unsure or need more information, speak to your GP, midwife, pharmacists, or practice nurse

3. How flu vaccines work

• Flu vaccines contain inactivated (killed) fragments of influenza viruses or weakened live influenza viruses (for nasal spray vaccines used in children) that cannot cause the disease itself
• Flu vaccines help your immune system to recognise and respond to influenza viruses
• After vaccination, your immune system produces protective proteins called antibodies that learn how to fight off the infection if encountered in the future
• Flu vaccines cannot give you flu. Protection through vaccination helps to reduce the risk of becoming seriously unwell from flu, and can help reduce the risk of hospitalisation and complications

4. Types of flu vaccines

• There are several types of flu vaccines approved for use in the UK
• You will be offered the type most suitable for you or your child
• Types of flu vaccine include:

4.1 Inactivated flu vaccines (injection)

• Inactivated flu vaccines contain killed or purified components of the influenza virus that cannot cause the disease itself
• These vaccines are given as an injection in the upper arm and are suitable for most eligible adults, including those with weakened immune systems
• Most adults receive an inactivated flu vaccine

4.2 Live attenuated flu vaccines (nasal spray)

• Live attenuated flu vaccines contain a weakened influenza virus strain that cannot cause disease
• Children above the age of 2 years are usually offered the nasal spray flu vaccine, which is quick and painless, and is given as a single squirt up each nostril
• The nasal spray vaccine is not suitable for all children, including some with weakened immune systems or certain medical conditions. A suitable alternative will be offered where needed

5. Flu vaccines and pregnancy

• Studies have shown that pregnant individuals are at increased risk of complications from flu
• Flu vaccination during pregnancy helps protect both you and your baby from serious illness
• Flu vaccines have been used safely during pregnancy for many years
• Protection that the flu vaccine provides is passed on to your baby. This lasts for the first few months after their birth, when they’re particularly at risk from flu
• If you are pregnant and have questions about flu vaccination, speak to your GP, midwife, pharmacist or practice nurse. They can advise on the most appropriate vaccination for you

6. Safety and effectiveness of flu vaccines

• Vaccination is one of the safest and most effective ways to protect people at higher risk of serious illness from flu
• Seasonal flu vaccines lower the risk of illness, serious illness, hospitalisation or complications if you are exposed to the virus
• Millions of flu vaccines are safely given every year in the UK and around the world
• Flu vaccines used in the UK meet the MHRA’s strict standards for safety, quality, and effectiveness
• The MHRA monitors the safety and effectiveness of all flu vaccines through processes such as batch testing to ensure that each batch of products meets the quality standard defined by their marketing authorisations (product licences) before being used
• The MHRA regularly tracks and reviews adverse drug reaction reports through the Yellow Card scheme to ensure we have information on real world use of the vaccines

7. How flu vaccines are updated

• Influenza viruses change over time, which is why updated vaccines are needed each year
• Each year, scientists around the world work together to look at changes in flu viruses to work out which new flu virus strains are emerging
• The strains most likely to cause illness are identified before each flu season, and vaccines are updated to match them as closely as possible
• Even if the vaccine doesn’t perfectly match a strain, it usually provides some protection against it
• This global process helps to ensure that seasonal flu vaccines remain effective and up to date

8. Who should not receive the flu vaccine

• Most eligible individuals can safely receive the flu vaccine
• You should not receive the flu vaccine if you:
  • have had a severe allergic reaction (anaphylaxis) to a previous flu vaccine or any ingredient in the vaccine
  • have an allergy to any of the vaccine ingredients
  • have a high fever on the day of vaccination
• If you are unsure, speak to your GP, midwife, pharmacists, or practice nurse

9. Flu vaccine side effects

• The most common side effects of flu vaccines are usually mild and improve within a few days. These reactions are signs that your immune system is responding to the vaccine
• Common side effects of the injected flu vaccine may include:
  • soreness, redness or swelling at the injection site
  • fever
  • tiredness
  • headache
  • muscle or joint aches
  • feeling generally unwell for a short time
• Side effects of the nasal spray flu vaccine may commonly include:
  • a runny or blocked nose
  • headache
  • tiredness
  • some loss of appetite
• These symptoms usually improve within a few days. If symptoms continue or you are concerned, speak to your GP, midwife, pharmacist, or practice nurse
• Serious allergic reactions (anaphylaxis) after vaccination are very rare. The person giving the vaccine will be trained to recognise and treat allergic reactions immediately

10. Less common side effects

• The risk of serious side effects is very low, and the benefits of vaccination far outweigh any potential risks
• Very rare reports of Guillain-Barré syndrome and worsening of symptoms of Leigh syndrome (mitochondrial encephalomyopathy) have been reported

11. Report side effects to the Yellow Card scheme

• You should report any suspected side effects of vaccination to the MHRA via a Yellow Card to:
• the Yellow Card website
• the Yellow Card app; download from the Apple App Store or Google Play Store
• Reports help us gain a better understanding of vaccine interactions and safeguard patients through vigilant monitoring