- Passive immunity is formed via the introduction of antibodies into an individual from an external source.
- No direct contact with the pathogen or it's antigen is needed to generate immunity.
- The antibodies aren't being produced by the individual so, they aren't replaced when they're broken down. No memory cells so, no long-lasting immunity.
E.g. Anti-venom given to snake bite victims. OR The immunity obtained by the embryo when the antibodies pass across the placenta.
Active immunity is formed from direct contact with the pathogen or it's antigen. It involves the production of antibodies through the individuals own immune system.
Immunity takes time to develop, it's long-lasting and is of two forms:
- Natural active immunity - Results from a person becoming infected with a disease under normal circumstances and the body produces its own antibodies.
- Artificial active immunity - is essentially immunisations, involves stimulating an immune reponse, without the individual suffering symptoms of the disease.
When first vaccinated, the response is minimal because only a small amount of dead or weakened antigen is injected into the body. However the crucial part being that memory cells are formed, these ensure that if infected by the same pathogen in the future they can divide rapidly into plasma cells and secrete their antibody. Resulting in little or no side effects shown.
Herd immunity is essentially just the majority of the immunised population protecting the vulnerable minority that aren't immune.
In a more perplex text book fashion:
Its when a large amount of the population is immunised and therefore will not acquire the disease, therefore are unable to contaminate the vulnerable minority who are not immune. E.g. babies with weak immune systems OR unwell patients with vulnerable immune systems.
Features of a successful vaccine programme
There have been past exam questions on the features of a successful vaccine programme
- A suitable vaccine must be economically available in sufficient quantities to immunise msot of the vulnerable population
- There must be few side effects. Unpleasant side-effects may discourage individuals in the population from being vaccinated.
- Storage, production, and transportation facilities must be readily available
- Must be the means of administering the vaccine properly at appropriate times within available centres across the population.
- It must be possible to immunise the vast majority of the population to produce herd immunity.