Inactivated Flu Vaccine

Inactivated flu vaccine

Influenza (flu) is a very common and highly infectious disease caused by a virus. It is much more severe than the common cold and often results in at least 2-3 days in bed, leading to missed work and school days. For some at-risk groups, flu can be very dangerous. Flu complications lead to tens of thousands of hospital stays and an average of 600 deaths in the UK every year. 

This page provides information about:

  • Key facts about the inactivated flu vaccine
  • Who is eligible and how to get the vaccine?
  • How effective is the NHS flu immunisation programme?
  • Gigi’s story – long term effects of flu
  • Why do we need the flu vaccine every year?
  • Safety and side effects
  • Ingredients

Key vaccine facts

In the UK the flu vaccine is available each year from late September or early October onwards. It is recommended to get the flu vaccine in the autumn, before outbreaks of flu have started. It takes up to two weeks after vaccination for you to be protected against flu. In the 2020-21 season, more than 19 million adults and children were vaccinated against flu across the UK, over 80% of those offered the vaccination.

The inactivated flu vaccine does not contain any live flu viruses and cannot give you flu. In the 2022-23 season, three different types of inactivated flu vaccine will be offered in the UK, as well as the nasal flu vaccine.



Who should have the vaccine?

In the 2022/23 flu season, the flu vaccine will be available for free to the following groups in England:

  • All children aged 2 to 10 years on 31st Aug 2022 (see Nasal Flu vaccine)
  • Secondary school children in years 7, 8 and 9 - any remaining vaccine will be offered to children in years 10 and 11, subject to vaccine availability
  • Those aged 50-64 years
  • Those aged 65 years or over 
  • Pregnant women (see Flu Vaccine in Pregnancy)
  • Those in long-term residential care homes
  • Carers
  • Frontline health and social care workers
  • Close contacts of immunocompromised individuals
  • Those aged 6 months to 65 years in at-risk groups including people with the following health conditions:
    • Respiratory (lung) diseases, including asthma
    • Heart disease, kidney disease or liver disease
    • Neurological (brain or nerve) conditions including learning disability
    • Diabetes (see a short film of a woman with Type 1 diabetes talking about why she gets the flu vaccine)
    • A severely weakened immune system (immunosuppression), a missing spleen, sickle cell anaemia or coeliac disease
    • Being seriously overweight (BMI of 40 and above)

Your doctor may recommend the flu vaccine in other circumstances as well.

Note that the eligibility criteria for the 2022/23 season are different to those in the 2021/22 season, so some people who were eligible for the flu vaccine last year may not be eligible this year.

Babies under 6 months old are too young to receive a flu vaccine. This is because they have maternal antibodies passed on from their mother which prevent the vaccine from working so well. Flu vaccination is offered to all pregnant women in the UK (see Flu Vaccine in Pregnancy). As well as protecting pregnant women themselves, this also helps to protect their newborn babies from flu.

How effective is the NHS flu immunisation programme?

The flu vaccine works better in some years than others (see ‘Why do we need the flu vaccine every year?’ below). Across all age groups including children, the flu vaccine prevented 15-52% of flu cases between 2015 - 2020 (see research by Public Health England on the effectiveness of flu vaccines in the 2015-16 season2016-17 season2017-18 season2018-19 season and 2019-20 season). Due to low levels of circulating influenza in the 2020-21 flu season, it has not been possible to determine vaccine effectiveness for this time period.  

​ Bar chart of annual flu vaccine effectiveness (%) between 2015 and 2020. Data shown for both children aged 2-17 and all ages with effectiveness ranging from 15% to 65.8%.

Protection from the flu virus varies for different age groups. In children aged 2-17, the flu vaccine prevented 66% of flu cases in 2016-17, 27% of flu cases in 2017-18, and 49% of flu cases in 2018-19. However, in the over 65 age group the inactivated flu vaccine worked less well than it did in other adults and children. In 2016-17, the data suggest that the inactivated flu vaccine did not work at all in people aged over 65, whilst in 2017-2018 it resulted in slightly better results in that age group. Due to the lower effectiveness of the inactivated flu vaccine in older people, a vaccine containing an adjuvant was introduced for the 2018-19 season. This is a substance that strengthens and lengthens the immune response to the vaccine and resulted in better prevention of flu in people aged 65 or over in flu seasons since 2018-19. The adjuvanted vaccine is still recommended for this age group in the 2022-23 season.

It is not understood why flu vaccines do not work so well in older adults. However, this reinforces the importance of vaccinating children and healthcare workers, both of whom can help to stop the spread of flu to older adults. 

Gigi’s story – long term effects of flu

Gigi ended up in intensive care after coming down with flu and has been left with long-term effects. Grateful thanks to Shot by Shot for permission to use this film.

Safety and side effects

The inactivated flu vaccine does not contain the live virus and cannot cause flu. Flu vaccines have a very good safety record. The most commonly reported side effects of flu vaccines are:

  • pain, swelling, bruising, hardness or redness at the injection site
  • slightly raised temperature (fever)
  • headache
  • sweating
  • aching joints or muscles
  • shivering
  • tiredness
  • feeling generally unwell

A higher rate of these common side effects has been reported with Fluad, an adjuvanted trivalent vaccine (aTIV) which was recommended for people aged 65 and over in previous years. This year, a quadrivalent inactivated influenza vaccine which also uses an adjuvant (aQIV) is being offered to people aged over 65. Side effects usually last 1-3 days. 

There are several different makes of flu vaccine available each year. For more information on side effects, ask for the Patient Information Leaflet for the vaccine you are offered. Additional information about vaccine side effects, anaphylaxis and adverse reactions can be found here.

Why do we need the flu vaccine every year?

Flu vaccines have an excellent safety record. They are the best protection we have against an unpredictable virus which can cause severe illness and deaths each year among at-risk groups. It is important to have a flu vaccine every year because the flu virus is very variable and changes over time. Each year there are different strains around, and a new vaccine has to be prepared to deal with them. Vaccination from previous years is not likely to protect people against current strains of flu. 

Each year’s flu vaccine is made to give the best protection against the strains of flu that are expected to circulate in the coming season. The trivalent vaccine protects against three of the flu virus strains which are most likely to be around. The quadrivalent vaccine protects against four flu virus strains. However, decisions about what to put in the flu vaccine have to be made six months before the flu season starts. 

Every February in the Northern Hemisphere, the World Health Organization (WHO) reviews the types of flu that have been circulating in all parts of the world and chooses the ones which will go into the vaccine for the following autumn. This allows time for the vaccine to be made – but it also gives the flu virus time to change before vaccination starts in the autumn. This means that sometimes the flu vaccine may not be a good match for all the strains of flu that are circulating. Read more about the WHO recommendations for the 2022-23 season.

Researchers are investigating ways to create a flu vaccine that protects against all the many different varieties of flu. If they are successful, it will mean that people will only need a single flu vaccine to give them lifelong protection, instead of having a yearly vaccine. However, it will be several years before we find out if it is possible to do this.

The viruses for flu vaccines are usually grown in hen’s eggs. This is a slow process and can lead to something called ‘egg adaptation’. The flu virus strain starts to adapt to the conditions in the egg, leading to changes in the virus. This is another reason that the flu vaccine may not always match the circulating strains of flu. For flu seasons since 2018-19, a new vaccine has been developed using cell culture instead of eggs. This vaccine is less likely to adapt as it has been developed using cells that are very similar to human cells.


Several different brands of flu vaccine are used in the UK each flu season. For full information on ingredients, ask for the Patient Information Leaflet for the vaccine you are offered or look the brand name up on the electronic Medicines Compendium (eMC).

Inactivated flu vaccines usually contain very small amounts of egg proteins (ovalbumin), as the virus is often grown on hens’ eggs. People who are allergic to eggs should ask their doctor for advice. With specialist medical advice, they may be able to receive a vaccine with a very low ovalbumin content or the cell-based quadrivalent vaccine as an alternative to those grown on eggs. See more information on egg proteins in vaccines. The UK Health Security Agency (UKHSA) produce an information sheet showing the ovalbumin content of flu vaccines in the current flu season.

Inactivated flu vaccines used in the UK often contain very small amounts of the following ingredients:

The vaccine recommended for people aged 65 and over, contains a small amount of an adjuvant called MF59. Adjuvants are substances which help to strengthen and lengthen the immune response to the vaccine. The main ingredient in MF59 is squalene oil, a naturally-occurring oil found in humans, plants and animals.

Flu vaccines may also contain tiny traces of these products used during the manufacturing process:

  • antibiotics (gentamicin, neomycin, kanamycin or polymyxin), used to stop bacteria growing and contaminating the vaccine
  • formaldehyde, an organic compound used to inactivate (kill) the viruses
Page last updated: 
Tuesday, July 26, 2022


Influenza (flu)

Influenza (flu) is a very common, highly infectious disease caused by a virus. It can be very... Read more