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Vaccination and Immunity

Immunological Memory

After an immune response, memory cells are produced. These lay dormant in the lymphatic system for many years, if they detect a pathogen with the specific antigen they can clone rapidly and sectrete antibodies. This means that secondary exposure to a pathogen produces a much more rapid secondary response which means you are not as badly affected the second time the virus appears - this is important in vaccination. See the image below.

graph of primary and secondary responses

You might think it odd then, that we can suffer from flu several times. The reason is that there are different types: influenza type A, B and C and within these types there are various strains. The variation in pathogens means that it is difficult to get immunity to many pathogens.


A vaccine takes advantage of the secondary response effect. It contains antigen from pathogens, and this induces the production of memory cells - giving protection from infection by that organism.

There are several types of vaccine used, these are:

Name and ExampleProduction
Killed virulent organisms
Whooping cough
The pathogen is killed and the antigens remain so an immune response is induced without the pathogen spreading.
Live non-virulent strains
A strain of pathogen that doesn't cause disease but still causes antibody production.
Modified toxins
A modified version of toxin treated with heat or chemicals, shouldn't produce symptoms but still triggers a response.
Isolated antigens from a pathogen
The antigen is seperated from the pathogen and injected seperately.
Genetically engineered antigens
Hepatitis B
The antigens have been isolated and made by genetic engineering, are injected without the virus.

Passive Immunity

This is when the antibodies themselves are given to prevent infection. This occurs naturally for babies when a type of milk called colostrum is produced by mothers that contains lots of antibodies. Passive immunity can also be artificially induced if someone is given (by injection) some antibody.

Passive immunity is only temporary and will last a few months at most, this is because they are not your own antibodies and they will be removed by the body.