Immunity is the body's ability to defend itself against infections diseases. The human immune system is very complex but can be broadly categorised into the following two parts.

Innate Immunity

This is the natural form of immunity from birth. It has two parts:

1. Physical barriers e.g. the skin and mucous membranes
2. Chemical barriers e.g. digestive enzymes and antimicrobial proteins

Acquired Immunity

This develops over the course of an individual's life. It's built through exposure to infections or vaccinations and enables the body to recognise and respond more effectively to specific pathogens in the future.

Acquired immunity can be created actively or passively.

Passive immunity is when the body receives antibodies to a disease rather than the body creating the antibodies itself.

Examples include: newborn babies acquiring antibodies from the mother through the placenta or people being given antibody-containing blood products such as immunoglobulins.

Passive immunity creates immediate protection from a disease but only lasts a few weeks or months.

Active immunity is when the body is exposed to a pathogen and the immune system creates antibodies for that disease. We can either expose the body naturally (when someone gets the actual disease) or through vaccinations (when the body is exposed to a weakened/inactive or dead form of the pathogen). Once the body has been exposed, when it comes into contact with the pathogen again, it will recognise it and produce the required antibodies.

Active immunity takes longer to produce but is much longer lasting than passive immunity.