Vaccines need additives to improve the way they work and increase their shelf life (how long they can be kept for). The three main substances added to vaccines are:
adjuvants or enhancers – to make the vaccine more effective by stimulating your immune system, making it respond quicker and more strongly to the vaccine
stabilisers – to stop the vaccine deteriorating when it is exposed to changes in the environment, such as light and temperature
preservatives – to increase the vaccine’s shelf life
Find more detailed information about vaccine ingredients.