What are Vaccines?
A vaccine is a biological preparation that improves protection to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins or one of its surface proteins.
The agent stimulates the body’s immune system to recognise the agent as foreign, destroy it, and ‘remember’ it, so that the immune system can more easily recognise and destroy any of these microorganisms that it later encounters, before a person becomes unwell.
Immunity can be divided into active immunity and passive immunity. Active immunity is the production of antibodies against a specific disease by the immune system. It can be acquired in two ways, either by contracting the disease or through vaccination. Passive immunity is protection against disease through antibodies produced by another human being or animal. Passive immunity is effective, but protection is generally limited and diminishes over time (usually a few weeks or months).
Watch this animation made by the Oxford Vaccine Group showing how vaccines work:
This is an additional video, hosted on YouTube.