How flu vaccines works

When a flu vaccine is given it stimulates your body's immune system to make antibodies to attack the flu viruses that are contained in the vaccine.

Antibodies are proteins that recognise and fight off germs, such as viruses, that have invaded your blood. It can take up to 14 days for immunity to build up fully after having a flu vaccine, so it is important to have a flu vaccine before flu starts to circulate.

No vaccine is 100% effective, but if you're exposed to a flu virus after you've had a flu vaccine, if the strain is one that was in the vaccine, your immune system is likely to recognise the virus and produce antibodies to fight it.

If you are in a risk group you should have a flu vaccine every year, as the antibodies that protect you from flu decline over time, and the flu strains circulating in the community can also change from year to year.

How annual flu vaccines change

The flu virus constantly changes, so different strains circulate yearly. Each year, the flu viruses that are most likely to circulate and cause health problems are identified in advance and vaccines are made to match them as closely as possible. The vaccines are recommended by the World Health Organization (WHO), which monitors the vitus throughout the World.  Flu vaccines contain four strains of the virus.

Flu vaccination is offered annually because the previous year's vaccine may not provide protection against the strains that circulate in a new season. Immunity also needs to be boosted each year, even for the same strain. There are a number of different flu vaccines available again this season. The vaccine should provide protection throughout the current flu season. Information about the flu vaccine for 2023/24 can be found on the Flu Vaccination page.

Last Updated: 03/10/2023 10:59:08
The information on this page has been adapted by NHS Wales from original content supplied by NHS website nhs.uk