Vaccination

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Immunity is the ability of an organism to resist infection. It takes two forms: passive and active immunity.

Passive Immunity

Involves directly injecting a person with antibodies.

No contact with pathogen / antigens necessary to induce immunity - immunity is immediate.

Antibodies prepared from blood serum of infected human or animal or made by genetic engineering.

Antibodies not produced by individual so broken down and not replaced.

No memory cells made and no lasting immunity.

Active Immunity

Produced by stimulating production of antibodies by individual's immune system.

Direct contact with pathogen / antigen required.

Immunity takes a long time to develop.

Natural active immunity - individual becomes infected with disease under normal circumstances, body produces its own antibodies.

Artificial active immunity - vaccination or immunisation, induces immune response in individual without suffering symptoms of disease.

Vaccine is antigens, memory cells and weak, dead or non-virulent form of pathogen.

Stimulates production of antibodies and memory cells.

Vaccine administered through mouth or by injection.

Promotes primary immune response.

If infected with real virulent pathogen, more powerful secondary immune response triggered.

Pathogen killed before it can cause disease.

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How Vaccine is Made

Killed Virulent Organisms: pathogens grown in culture to create large number of cells, they are then killed but antigen is not denatured. Antigens on surface of pathogen trigger immune response without microbe causing damage. Danger that any surviving cells after treatment are still pathogenic.

Isolated Antigens From Pathogen: pathogens grown in culture to create large number of cells, cells then disrupted and antigen proteins isolated from cell membranes. Vaccine consists of antigens only and trigger immune response.

Modified Toxins (Toxoids): toxins produced by pathogens can act as antigens. Toxins purified and modified so no longer toxic but still function as antigens.

Some vaccines contain antigens to more than one pathogen.

Features of Successful Vaccination Programme

Vaccinations used as precautionary measure to prevent individuals from contracting disease.

Not used to treat the disease - when developing a vaccine, it must be:

Economically available to immunise most of the vulnerable population.

Have few side effects.

Must be easily produced, stored and transported.

Must be a means of administering the vaccine properly.

Must be possible to vaccinate majority of population (herd immunity).

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Herd Immunity

Arises when sufficiently large proportion of population has been vaccinated.

Makes it difficult for pathogen to spread within the population.

Pathogens passed from individual to individual when in close contact.

If vast majority of population immune, more difficult that infected individual will come in contact with vaccinated person.

Vaccinations may not eliminate disease:

May not induce immunity in certain individuals.

Individuals may develop disease immediately after vaccination before immunity levels are high enough.

Pathogen may mutate so its antigens change.

Impossible to make a vaccination against some pathogens.

Some pathogens 'hide' by concealing themselves inside cells or living in a place out of reach.

Individuals may object to vaccinations due to religion, ethics or medical reasons.

Ethics of Using Vaccines

Vaccines have side effects and sometimes cause long term harm - can risk of side effects be balanced against risk of developing the disease?

Can individual health risks from vaccination be balanced against advantages of controlling a disease for benefit of population at large?

Development of new vaccines often involves the use of animals - is this acceptable?

Is it acceptable to trial a new vaccine with unknown health risks only in a country where a targeted disease is common?

Should expensive vaccination programmes continue when a disease is almost eradicated?

On whom should vaccines be tested? How should trials be carried out?

To be fully effective, the majority of population should be vaccinated - should it be compulsory?