How do vaccines work?

A vaccine works by teaching your immune system how to recognise harmful microbes such as viruses and bacteria. The immune system produces antibodies against these harmful microbes that will recognise them any time you come into contact with them. If you are vaccinated then your immune system will respond quickly and effectively to prevent an infection because the antibodies act like a protective shield.

What is community or herd immunity?

Community immunity means that enough of the population are vaccinated to protect those who aren’t- for example, small babies who are too young to have received their vaccines, and people whose immune systems aren’t working effectively, such as those with cancer.
If you imagine a village with 100 people, and only two of them are vaccinated against a contagious disease, such as the flu, the other 98 people are very likely to become infected because they are surrounded by people coughing and sneezing and releasing the flu virus into the air around them. However, if 98 members of the village are vaccinated, they will effectively fight the infection and therefore won’t be coughing or sneezing over the 2 who can’t be vaccinated. It is community immunity that is responsible for wiping out diseases such as smallpox.

Types of vaccines

Live attenuated vaccines contain a weakened version of the virus or bacterium that causes disease. Because they contain the whole virus or bacterium they are very effective at teaching your immune system to recognise these infections if you ever encounter them. Because your immune system ‘sees’ the virus or bacterium it will remember it in the future, and these types of vaccines usually produce lifelong immunity after one or two doses, meaning that you won’t need boosters as you get older.

Live attenuated vaccines are usually created for viruses because they are easier to produce in the lab. One downside of live attenuated vaccines is that they always have to be kept in the fridge which can be a problem when delivering the vaccines to countries in developing countries.

An example of a live attenuated vaccine: Measles vaccine (part of the MMR vaccine)

Toxoid vaccines contain the toxins that are released by some types of bacteria. These toxins have been altered so that they don’t cause you any harm, but allow your immune system to learn to quickly respond to bacteria that release toxins into your bloodstream.

An example of a toxoid vaccine: Tetanus vaccine (part of the 6-in-1 vaccine)

Some bacteria are covered with complex sugar molecules which act as a mask over the bacteria so that it is difficult for the immune system to recognise that they may be harmful. Conjugate vaccines contain parts of the bacterium attached to some of these complex sugars, so that your immune system learns to recognise these sugars and therefore see past the ‘mask’ if you are contact with the bacteria in the future.

An example of a conjugate vaccine: The PCV vaccine

Inactivated vaccines contain dead virus or bacteria. The viruses and bacteria are killed in the lab by treatment with chemicals, heat or radiation and are very safe. Because they are dead they don’t produce as strong an immune response as live attenuated vaccines and so you will need several booster doses to make sure that your immune system remembers the virus or bacteria throughout your lifetime.

An example of an inactivated vaccine: Polio vaccine (part of the 6-in-1 vaccine)

Subunit vaccines contain parts of the bacteria or virus instead of the whole thing. Your immune system learns to recognise those parts and will respond to the whole virus or bacterium if it sees them in the future. They are very safe vaccines but do not produce quite as strong an immune response as live attenuated vaccines so usually you will need booster doses.

An example of a subunit vaccine: Hepatitis B vaccine (part of the 6-in-1 vaccine)