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. There are two different kinds of flu vaccine, both of which protect against common strains of seasonal flu:
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 2015-16 season, over 11 million adults and children in England got vaccinated against flu.
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:
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 people with:
Your doctor may recommend the flu vaccine in other circumstances as well. See a short film of a woman with Type 1 diabetes talking about why she gets the flu vaccine.
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.
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 and an information sheet from Public Health England showing the ovalbumin content of flu vaccines in the 2016/17 season .
None of the adult flu vaccines to be used in the UK in the 2016-2017 season contain the preservative thiomersal (mercury).
There are several different makes of flu vaccine available each year. For full information on ingredients, ask for the Patient Information Leaflet for the vaccine you are offered. Inactivated flu vaccines used in the UK often contain very small amounts of the following ingredients:
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.
'Flu isn't serious, so I don't need a flu vaccine' and 'I never get ill, so I don't need the vaccine'
It is tempting to think that flu is no worse than a bad cold, but in fact it is a serious disease which can infect anyone. For people at risk of complications, flu can lead to hospitalisation or even death. In rare cases flu can kill otherwise healthy people. 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. Even if you do not feel you need to protect yourself, getting the flu vaccine will help to reduce the spread of the disease, and so reduce the chance of passing on the flu virus to other people who may be at risk of flu. This is why the flu vaccine is recommended for all healthcare workers.
'The flu vaccine can give you flu'
This is not true. The inactivated flu vaccine does not contain any live flu viruses, so it cannot give you flu.
'Last year I had the flu vaccine but I got ill anyway, so it doesn't work'
No vaccine is 100% effective, including the flu vaccine. However, the vaccine usually prevents about half of all flu cases. Even if you do get flu after being vaccinated, the disease is often less severe than it would have been. It is important to remember that the flu vaccine only protects against flu, but there are other illnesses which have flu-like symptoms which you can still catch after getting the flu vaccine. It takes up to two weeks for the vaccine to take effect, so you could still catch flu if you are exposed to the virus during this time. Getting vaccinated as early as possible in the season can help to prevent this.
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 16 different types of the H protein, and 9 different types of the N protein. This means there are 144 different possibly varieties of Influenza A – from H1N1 (the Swine Flu virus) to H16N9. Not all of these types are known to infect humans, but there are still a lot of possible 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 occasionally the flu vaccine may not be a good match for all the strains of flu that are circulating.
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 will be possible to do this.