Vaccines Flashcards
What is passive immunity?
It’s produced by the introduction of antibodies into individuals from an outside source.
No direct contact with the pathogen or its antigen is necessary to induce immunity.
Immunity is acquired immediately.
As the antibodies are not being produced by the individuals themselves, the antibodies are not replaced when they are broken down, no memory cells are formed and so there is no lasting immunity.
What are examples of passive immunity?
Anti-venom given to victims of snake bites.
Immunity acquired by the foetus when antibodies pass across the placenta from the mother.
What is active immunity?
Immunity is the ability of an organism to resist infection.
It’s produced by stimulating the production of antibodies by the individual’s own immune system.
Direct contact with the pathogen or its antigen is necessary.
Immunity takes time to develop.
It is generally long lasting.
Has two types.
What is natural active immunity?
Results from an individual becoming infected with a disease under normal circumstances.
The body produces its own antibodies and may continue to do so for many years.
What is artificial active immunity?
Forms the basis of vaccination (immunisation).
It involves inducing an immune response in an individual, without them suffering the symptoms of the disease.
What is vaccination?
The introduction of the appropriate disease antigens into the body, either by injection or by mouth.
The intention is to stimulate an immune response against a particular disease.
How do vaccines work?
The antigens stimulate the immune response.
The response is slight because only a small amount of antigen has been introduced.
Memory cells are produced.
These remain in the blood and allow a greater, more immediate response to a future infection with the pathogen.
The result is that there is a rapid production of antibodies and the new infection is rapidly overcome before it can cause any harm, and with few symptoms.
When carried out on a large scale, this provides protection against disease for whole populations.
What is the success of a vaccination programme dependent on?
A suitable vaccine must be economically available in sufficient quantities to immunise most of the vulnerable population.
There must be few side effects, if any, from vaccination. Unpleasant side effects may discourage individuals from being vaccinated.
It must be possible to vaccinate the vast majority of the vulnerable population to produce herd immunity.
What is the success of a vaccination programme dependent on (logistical)?
Means of producing, storing and transporting the vaccine must be available. This usually involves technologically advanced equipment, hygienic conditions and refrigerated transport.
There must be the means of administering the vaccine properly at the appropriate time. This involves training staff with appropriate skills at different centres throughout the population.
What is herd immunity?
It arises when a sufficiently large proportion of the population has been vaccinated to make it difficult for a pathogen to spread within that population.
It is based on the idea that pathogens are passed from individual to individual when in close contact.
Where the vast majority of the population is immune, it is highly unlikely that a susceptible individual will come into contact with an infected person, protecting those not immune.
Why is herd immunity important?
It is never possible to vaccinate everyone in a large population.
For example, babies and very young children are not vaccinated because their immune system is not yet fully functional.
It could also be very dangerous to vaccinate those who are ill or have compromised immune systems.
How is herd immunity achieved?
The percentage of the population that must be vaccinated in order to achieve herd immunity is different for each disease.
To achieve it vaccination is best carried out at one time.
This means that, for a certain period, there are very few individuals in the population with the disease and the transmission of the pathogen is interrupted.
Why may vaccinations not eliminate a disease?
Vaccination fails to induce immunity in certain individuals, for example people with defective immune systems.
Individuals may develop the disease immediately after vaccination but before their immunity levels are high enough to prevent it. These individuals may harbour the pathogen and re-infect others.
Why may vaccinations not eliminate a disease - mutations?
The pathogen may mutate frequently, so that its antigens change suddenly rather than gradually.
This means that vaccines suddenly become ineffective because the new antigens on the pathogen are no longer recognised by the immune system.
As a result the immune system does not produce the antibodies to destroy the pathogen.
This antigenic variability happens within the influenza virus.
Immunity is therefore short-lived and individuals may develop repeated bouts of influenza during their lifetime.
Why may vaccinations not eliminate a disease - variety?
There may be so many varieties of a particular pathogen that it is almost impossible to develop a vaccine that is effective against them all.
For example, there are over 100 varieties of the common cold virus and new ones are constantly evolving.
Certain pathogens hide from the immune system, either by concealing themselves inside cells, or by living in places out of reach, such as in the intestines, for example the cholera pathogen.
