Inactivated Flu Vaccine

General information on flu vaccines in the UK

Influenza (flu) is a very common and highly infectious disease caused by a virus. It can be very dangerous, leading to serious complications and death, especially for people in risk groups. In rare cases flu can kill people who are otherwise healthy. In the UK an average of 600 people a year die from complications of flu, but in some years this can rise to over 10,000 people. Flu leads to hundreds of thousands of GP visits and tens of thousands of hospital stays a year. Apart from protecting individual people, getting the flu vaccine helps to reduce the spread of the disease, and so reduces the chance of passing on the flu virus to other people who may be at risk of flu.

There are two different kinds of flu vaccine, both of which protect against common strains of seasonal flu:

  • The inactivated flu vaccine (this page) is recommended for everyone aged 65 or over, pregnant women, people with certain medical conditions, people with learning disabilities, people living in a residential or nursing home, carers of people at risk of complications of the flu, healthcare professionals, and children aged 6 months to 2 years old who are at risk from complications of flu (including children with long-term health conditions such as asthma and other lung diseases, liver or kidney disease, brain conditions and learning disabilities).
  • The nasal flu vaccine is offered each year to children over the age of two.

Babies under 6 months old are too young to receive a flu vaccine. Flu vaccination is offered to all pregnant women in the UK (see Vaccines in Pregnancy: Flu). As well as protecting pregnant women themselves, this also helps to protect their newborn babies from flu.

In the 2016-17 season, more than 12.7 million adults and children in England got vaccinated against flu.

Key vaccine facts

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.

The inactivated flu vaccine does not contain any live flu viruses and cannot give you flu.

The vaccine is recommended for people in these groups:

  • Everyone aged 65 or over
  • Pregnant women (see Vaccines in Pregnancy: Flu for more information)
  • People with a medical condition (see list below)
  • People with learning disabilities (see the NHS easy-read leaflet for adults with learning disabilities )
  • People living in a residential or nursing home
  • Carers of people at risk of complications of the flu
  • Household contacts of people who are immunocompromised
  • Frontline health and social care workers
  • Children aged from 6 months to 2 years (i.e. too young for the nasal flu vaccine) who are at risk from complications of flu

Flu vaccines are recommended for people of all ages with some health conditions who are at greater risk of serious complications of flu. This includes:

  • 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.

Each year the vaccine protects against three of the strains which are most likely to be around. It usually prevents about half of all flu cases. The flu vaccine has an excellent safety record. It is still 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. See 'More information about the vaccine' (below) for more detail about the annual flu vaccine and how it is prepared.


There are several different makes of flu vaccine available each year. See a list of the flu vaccines to be used in the UK in the 2017-18 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 if there is an egg-free flu vaccine available. With specialist medical advice, they may also be able to receive a vaccine with a very low ovalbumin content. See more information on egg proteins in vaccines. Public Health England publish an information sheet showing the ovalbumin content of flu vaccines in the 2017-2018 season .

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

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

Side effects

The most commonly reported side effects of flu vaccines are: pain, swelling or redness at the injection site, slightly high temperature, headache, feeling a bit unwell, shivering, or tiredness. The inactivated flu vaccine does not contain any live viruses and cannot give you flu.

As with any vaccine, medicine or food, there is a very small chance of a severe allergic reaction (anaphylaxis). Anaphylaxis is different from less severe allergic reactions because it causes life-threatening breathing and/or circulation problems. It is always serious but can be treated with adrenaline. In the UK between 1997 and 2003 there were a total of 130 reports of anaphylaxis following ALL immunisations, but all of these people survived. Around 117 million doses of vaccines were given in the UK during this period, making the overall rate around 1 in 900,000. Depending on the cause of the reaction, and following expert guidance, the person may be able to have vaccinations in the future.

See more information on the monitoring of vaccine safety.

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. Reactions listed under ‘possible side effects’ or ‘adverse events’ on vaccine product information sheets may not all be directly linked to the vaccine. See Vaccine side effects and adverse reactions for more information on why this is the case.

More information about the vaccine

Why is it difficult to make flu vaccines?

Flu is a complicated virus. There are three basic types of flu: A, B and C. Type A is the most dangerous; it is the one that can cause serious disease and also triggers worldwide pandemics. Type C causes mild disease. Type B can make you feel very ill, but it has never led to a worldwide pandemic.

Type A is also much more complex than the other types of flu virus. On the surface of each Influenza A virus there are proteins that help the virus to invade cells. There are two kinds of protein: haemagglutinin and neuraminidase (referred to as H and N). There are 18 known different types of the H protein, and 11 known different types of the N protein. This means there are 198 different possible varieties of Influenza A – from H1N1 (the Swine Flu virus) to H18N11. Not all of these types are known to infect humans, but there are still a lot of options when it comes to designing the annual flu vaccine.

In addition, the flu virus can change quickly and easily. Each of the 144 types of Influenza A can undergo ‘antigenic drift’ – a process of genetic change that leads to even more variety within each type. Two different virus strains can even combine their genetic material to make a new sub-strain (this process is called ‘antigenic shift’, and is what led to the new Swine Flu virus in 2009).

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. 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 in 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. In about 9 out of 10 years the vaccine matches the strains causing illness that winter, but sometimes the flu virus changes in ways that are not expected. This means that sometimes the flu vaccine may not be a good match for all the strains of flu that are circulating.

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.

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 getting a yearly vaccine. However, it will be several years before we find out if it is possible to do this.

Does the vaccine work?

The flu vaccine works better in some years than others (see ‘Why is it difficult to make flu vaccines?’ above). Across all age groups including children, the flu vaccine prevented 52.4% of flu cases in 2015-16, and 39.8% of flu cases in 2016-17 (see research by Public Health England on the effectiveness of flu vaccines in the 2015-16 season and in the 2016-17 season ). However, protection varies for different age groups, and also against different strains of the virus. In 2015-16 the inactivated flu vaccine worked less well in the over 65 age group than it did in other adults and in children. In 2016-17, provisional data suggest that the inactivated flu vaccine did not work at all in the over 65 age group. It is not understood why the vaccine doesn’t work so well in older adults. This reinforces the importance of vaccinating children and healthcare workers, both of whom can help to stop the spread of flu to older adults.

The JCVI (Joint Committee on Vaccination and Immunisation), which advises the UK government on vaccination issues, is considering alternative influenza vaccines that might be better at protecting older adults. One of these contains an adjuvant (a substance which helps to strengthen and lengthen the immune response to the vaccine). In clinical trials, this vaccine has been shown to work better in older adults.

Page last updated: 
Thursday, February 8, 2018


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