Recent headlines have claimed that this year’s flu vaccine is only 3% effective. But what lies behind this statistic, and why is it important to get vaccinated against flu?
1. Flu is dangerous.
It is tempting to think that flu is no worse than a bad cold, but in fact it is a serious disease that 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. This in itself is a good reason for getting the flu vaccine, even if the protection it offers varies from year to year.
2. In 9 out of 10 years, the flu vaccine prevents about half of all flu cases.
A vaccine that is 50% effective may not sound good enough – but it prevents hundreds of thousands of people in the UK from getting sick.
3. The adult flu vaccine protects against three different strains of flu.
In the 2014-15 season, one of the strains in the adult flu vaccine did not offer very good protection against the main strain of flu causing disease in the UK. This is why the vaccine has been described as ‘only 3% effective’ in adults. However, it is believed that the vaccine has still offered some protection against this strain, especially in terms of preventing serious illness resulting in hospitalisation and death. In addition, the vaccine contained two other strains of flu virus, which protect against other strains of flu (Swine Flu and Influenza B, which could also have been circulating this winter). With a disease as serious as flu, even a small amount of protection is better than none.
4. The children’s Nasal Flu vaccine may have been more effective than the adult flu vaccine in the 2014-15 season, and helped to protect others.
The nasal flu vaccine is a different type of vaccine from the one used in adults. This season it had an additional strain of flu vaccine included, and offered protection against four strains of virus, not just three. In Autumn 2014 several areas of the UK ran pilot flu vaccination projects with all children of primary school age. In these areas, there have been fewer cases of flu overall. This suggests that giving more young children the Nasal Flu vaccine helps to protect everyone in the community, and it may be that the children’s flu vaccine was much more than 3% effective this year.
5. 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, including older people, pregnant women and those with a long-term health condition.
More information: 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 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. This is to allow time for the vaccine to be made – but it also means that there is time for the flu virus to change before vaccination starts in the autumn, which is what happened in 2014-15.
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. 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. In 2014 WHO predicted that the H2N3 variety of Influenza A would be circulating. They were right – but then the H2N3 virus went through an ‘antigenic drift’ which meant that the vaccine did not quite match the virus, and so was not very effective at fighting it.
However, as stated above, the vaccine did still offer some protection. And just because the adult flu vaccine didn’t work very well in 2014-15, it doesn’t mean that the 2015-16 vaccine will be ineffective. In fact the children’s nasal flu vaccine may even help to provide protection for future years, by priming the immune system to respond more strongly the next time the vaccine is given.
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.