Seasonal influenza is a very common and highly infectious disease caused by a virus. It can be much more severe than the common cold and may result in two or three 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, however this can vary In 2012, there were 83 deaths from influenza in England and Wales, whereas in 2018, there were 1598 deaths.
The flu virus changes constantly, which means that different strains circulate each year. The World Health Organization monitors the virus throughout the world and advises which strain should be included in an annual flu vaccine. Flu vaccination is offered annually because the previous year's vaccine may not provide protection.
In the UK, the flu vaccine is available each year from late September or early October onwards. People who are eligible are recommended to get their flu vaccine in the autumn or early winter, before outbreaks begin. It takes up to two weeks after vaccination for protection against flu to develop.
Ideally, people should have received their vaccination by the end of December, although there can still be some benefit to offer vaccination until the end of March, as flu can continue to circulate.
In the 2022-23 season, three different types of inactivated flu vaccine are available - QIVe, QIVc, and QIVr. As well as the nasal flu vaccine – LAIV.
A separate version of the vaccine, aQIV, is also available for older people. This has added ‘adjuvant’ to make the vaccine more effective in older people. All of these vaccines are ‘quadrivalent’ and protect against four strains of the flu.
See table in ‘more information’ below to find out which vaccine is recommended for each age group.
Flu vaccine (inactivated)
In the UK the groups of people recommended for vaccination against flu is subject to change annually. In the 2022/23 flu season, the following people are eligible to receive the flu vaccine free of charge:
Your doctor may recommend the flu vaccine in other circumstances as well.
Babies under 6 months old are too young to receive a flu vaccine. This is because they have maternal antibodies passed on which prevent the vaccine from working so well. Flu vaccination is offered to all pregnant people in the UK (see Flu Vaccine in Pregnancy). As well as protecting the pregnant person themselves, this also helps to protect their newborn babies from flu.
In the 2020-21 season, more than 19 million adults and children were vaccinated against flu across the UK. Please see 'Who should have the vaccine' for more detail.
All vaccines go through rigorous testing and regulatory processes that can take up to 15 years to ensure they are safe and effective. Like all medicines, vaccines can cause side effects, but not everyone experiences them.
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:
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. An adjuvanted vaccine has an ingredient added to it to create a stronger immune response. Fluad is designed to protect against three strains of flu (trivalent).
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 one to three days. This is designed to protect against four strains and contains no live virus.
There are several different flu vaccines 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.
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 specialist advice. They may be able to receive a vaccine with a very low ovalbumin content or a quadrivalent vaccine that has been grown on mammal cells, as an alternative.
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:
LAIV, the flu vaccine recommended for Children aged 2-10 years, contains a highly processed form of porcine gelatine. It is used as a stabiliser to protect the live viruses from the effects of temperature. Very sensitive tests have shown that no DNA from pigs can be found in the LAIV vaccine.
Recommended flu vaccines
In the 2022-23 season, three different types of inactivated flu vaccine are available - QIVe, QIVc, and QIVr. QIV is a shortened version of 'quadrivalent influenza vaccine’ – this means the influenza vaccines are quadrivalent and protect you against four different strains of influenza.
The three main types of QIV are ‘e’,’c’, or ‘r’. ‘E' is a shorter version of egg-based, ‘c’ is a shorter version of cell based, and ‘r’ is short for recombinant (made using an insect cell line). There is also one other type of QIVe available for older people, this is called aQIV. The ‘a’ is short for ‘adjuvanted’ and this means an ‘adjuvant’ has been added to make the vaccine more effective in older people.
Finally, the nasal flu vaccine – LAIV is available for children aged 2-10 years. LAIV is short for ‘live attenuated influenza vaccine’, which means the vaccine contains whole viruses which have been ‘weakened’ to create an immune response without causing disease in healthy people.
For more information about types of vaccines, visit https://vk.web.ox.ac.uk/types-of-vaccine, or see the table below to find out which influenza vaccine is recommended for each age group.
How effective is the NHS flu immunisation programme?
The flu vaccine works better in some years than others. Across all age groups including children, the flu vaccine prevented between 15 to 52% of flu cases between 2015 - 2020 For the breakdowns of each year, please consult Public Health England's data on the effectiveness of flu vaccines in the 2015-16 season, 2016-17 season, 2017-18 season, 2018-19 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.
Click here for an accessible text version of this graph
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. The people taking part in these studies were patients who had visited their general practitioner (GP) during the study period with flu-like symptoms.
However, in the over 65 age group the inactivated flu vaccine worked less well than it did in other groups. 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.
To address this problem of lower effectiveness in older people, an inactivated vaccine containing an adjuvant was introduced for the 2018-19 season. This is a substance that strengthens and lengthens the immune response. It has 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. As well as protecting others, you will also be protecting yourself against getting the flu, or from experiencing severe symptoms.
Why do we need the flu vaccine every year?
It is important to have a flu vaccine every year because the flu virus is variable and changes over time. Each year there are different strains 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.
Click here for an accessible text version of this infographic
Each year’s flu vaccine is made to give the best protection against the strains of flu that are expected to circulate (spread) 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, the World Health Organisation (WHO) reviews the types of flu that have been circulating in all parts of the world and decides which ones 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 virus for the QIVe flu vaccine is 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. Cell based vaccines are now the recommended vaccines for people over two years, unless the recommended vaccine is not suitable or unavailable. For example, due to porcine gelatine content.