What is a vaccine?

This video explains how vaccines help our bodies to recognise and fight diseases. You can learn more at the Vaccine Knowledge Project website:

How do vaccines work?

A vaccine is a preparation that is used to stimulate the body’s immune response against diseases.

Live vaccines are active vaccines such as attenuated strains that replicate in a host. The pathogen, such as virus or bacterium, has been weakened to reduce virulence to cause none or very mild disease in healthy people, which acts like a natural infection. Live vaccines stimulate the closest response to actual infection and therefore elicit good, strong, long-lasting immune responses.

A non-live vaccine does not have any live biological material and can’t cause the disease it is protecting. An adjuvant (substance used to increase the immune response to the vaccine) is required, and several doses of inactivated vaccines may be required to evoke a sufficient immune response.

Some examples of these are highlighted below:

• Inactivated vaccines: suspensions of whole intact killed pathogens e.g. whole-cell pertussis (bacteria), inactivated poliovirus
• Sub-unit vaccines: contain one or a few components (sub-units) of the pathogen which is important in protection e.g. hepatitis B vaccine which uses only surface proteins of the virus
• Conjugate vaccines: These conjugate a poorly immunogenic antigen and a protein carrier that is highly immunogenic, providing a lasting immune response e.g. Haemophilus influenzae B (Hib) vaccine uses bacterial polysaccharides combined to its capsule proteins
• Toxoid vaccines: based on the toxin produced by bacteria that evades the bloodstream and causes most of the disease symptoms e.g. Tetanus and diphtheria vaccines
• mRNA vaccine: Messenger RNA (mRNA) vaccines give information to cells on how to make a protein that will trigger an immune response e.g. SARS-CoV-2 vaccine

Share other examples of vaccines in the comments section