What are vaccines and how do they work?
Vaccines train your body to recognise and fight off infections which may be caused by viruses, bacteria or parasites. They are a preventative medicine that protects you from infectious diseases by helping your immune system to prepare its defences before an infection strikes. In most cases, this means we are either completely protected from the disease or don’t fall seriously ill when we do catch the infection. Each vaccine is designed to target a particular microbe (virus, bacteria or parasite). By completely blocking or reducing the amount of infection in your system and the time it is there for, most vaccines also reduce the risk of passing on the illness to other people you are spending time with, including friends and family.
Your body is protected by your immune system that hunts down and destroys invading viruses, bacteria or parasites that might cause you harm. But when your immune system first encounters these microbes, it takes a while to recognise the threat and mount a defence against it. This means you may fall ill with the disease while waiting for your body to fight back.
Once your body has learned to recognise a particular microbe, your immune system responds faster and better at protecting you next time, meaning you will either remain completely well or not get as ill.
Vaccines use weakened or dead versions of viruses, bacteria or parasites, or parts of them, known as antigens. Your immune system detects these antigens and responds to them, memorising them in the process
Vaccines are usually administered by an injection, or sometimes by oral drops or a nasal spray, depending on the type of vaccine, who it is being given to, and where in the body it is most likely to stimulate our immune system to mount the best defence.
It can sometimes take several doses to train your immune system to recognise a microbe, especially in babies and young children. Later in life, booster vaccines can serve as prompts to remind your immune system of what it once knew well.
We currently have vaccines that work against viruses – like those that cause Covid-19, flu or measles – and bacteria, such as those that cause meningitis and whooping cough. In 2021 the first ever vaccine against a parasite – malaria – was recommended for use by the World Health Organization. Some vaccines even protect against specific cancers by preventing infections by viruses such as human papillomavirus (HPV) and hepatitis B virus, which can cause cancers in later life.