3.2.4: Cell recognition and the immune system (Vaccination and immunity)

Immunity is the ability of an organism to resist infection. It can take two forms:

• Active immunity: This is produced by stimulating the production of antibodies by the individuals own immune system by direct contact with the pathogen/antigen. It is generally longer lasting but takes time to develop. There are two kinds of active immunity:
• Artificial active immunity: occurs from immunisation (vaccination). Involves inducing an immune response in an individual without suffering the disease. E.g injecting a dead/inactive form of the pathogen
• Natural active immunity: results from an individual becoming infected with a disease. E.g if I was to obtain a cold my plasma B cells would produce antibodies
• Passive immunity: This is produced by the introduction of antibodies into individuals from an outside source - direct contact with the antigen/pathogen is not required and immunity develops immediately. However, as the body is not producing its own antibodies, the antibodies are not replaced and no memory cells form. This means that immunity is not long lasting. Examples include anti-venom given to victims of snake bites, and antibodies given to baba from mama.

Vaccination involves stimulating an immune response by injecting/swallowing a vaccine. A vaccine contains one or more types of antigen of the appropriate disease. The initial (primary) response is only little but memory cells are produced (this is the important bit!!). These memory cells remain in the blood (humour) and divide, by mitosis, producing plasma B cells and more memory cells if a future infection is detected.

Vaccines must be economically available in sufficient quantities to immunise at least most of the vulnerable population. There must also be few side affects and a means of producing/storing/transporting/administering the vaccine.

Herd immunity

This arrises when a large proportion of the population has been vaccinated. For a pathogen to spread, it must be passed from person to person in close proximity. Since the vast majority of the population are immune, it is very unlikely that a susceptible person comes into contact with another susceptible person - this means that those not vaccinated are still protected from the disease. It is important as not all of the community may be vaccinated. For example, babies are not vaccinated as their immune systems are still developing, individuals may be allergic to an ingredient in the vaccine.

NOTE: it is important to understand that vaccination does not eliminate a disease. For example, as mentioned above, not all individuals can be vaccinated. Also, someone may obtain the disease straight after vaccination when their immunity is not high enough. Also, antigenic variability. 

Vaccine ethics:

Some individuals may have objections to vaccinations for religious/ethical/medical reasons...

• Vaccines have side effects that may cause long term harm
• How should we test vaccines?
• Is it acceptable to involve the use of animals in the production and development of existing/new vaccines?
• It is right that, in the interest of everyone's health, all of the population should be vaccinated (regardless of religious reasons etc)? - basically, should vaccination be compulsory?
• Should expensive vaccination programmes be stopped if the disease is almost eradicated?