Immunisation Flashcards
Define the term:
Immunisation
a susceptible individual now has protection from infection
This can include the ability to prevent an infection entirely, or more commonly, preventing severe symptoms and death
Define the term:
Vaccination
The physical process of giving a vaccine
Often used interchangeably with “immunisation”
Define the term:
Immunogenicity
The ability to provoke an immune response
We want a vaccine to significantly stimulate an immune response. However over-stimulating an immune response often causes vaccine side effects such as fatigue, fever, pain at site of entry etc
Define the term:
Infection
Invasion and multiplication of a microbe in the body
A person can be infected, but might not have any overt symptoms of this. They would be termed asymptomatic
Define the term:
Disease
Note it is similar to “infection”, but with an important change:
an infection, which causes damage to the host, resulting in symptoms
What are the broad aims of immunisation?
Prevent infection - when the immune system encounters the pathogen in the future, it may be able to terminate infection early. Thereby preventing symptoms developing
Prevent disease - by preventing significant damage to the body, the patient will have less symptoms. This means they will be less likely to require hospital admission or die
Prevent spread - by preventing infections, and reducing disease, there will be less symptomatic patients. This helps reduce transmission of infection. For example, if a vaccine reduces Influenza symptoms, it means that patients will cough less. And therefore means it is less likely to be transmitted to susceptible individuals. Vaccines can be used in outbreak settings to help control or terminate the outbreak
Eradication - some pathogens infect humans only, and would be suitable to be eradicated, if every person was vaccinated. To date, only Smallpox has been eradicated.
Broadly speaking, when are vaccines commonly administered to patients?
Pre-exposure -
- routine childhood immunisation schedule
- routine elderly e.g influenza annually
- pregnancy - pertussis, influenza
- high risk patients - immunosuppressed, occupational risks, travel related risks
Post exposure -
- following high risk exposure e.g Hepatitis B, Rabies
- outbreak control e.g Hepatitis A
What are contra-indications to immunisation?
Absolute contra-indications:
- anaphylaxis to previous vaccine
- immunosuppression (some vaccines)
- pregnancy (some vaccines)
Relative contra-indications:
- if patient unwell with fever
- if other vaccines given recently - immune response will be blunted if it has recently been stimulated. Usually recommend at least 4 weeks between vaccines in general. Although some can be given together
- immunoglobulin therapy - if patient has recently had immunoglobulin, then this will neutralise any vaccine components. Therefore the immune response will not be stimulated, and no memory will be developed
Why do vaccines sometimes “fail”?
Misinterpretation of what a vaccine “failure” is. It should protect against death firstly, and also prevent severe disease and hospitalisation. It cannot fully prevent against the acquisition of infection. For example, someone has had their influenza vaccine. A few weeks later they developed cold-like symptoms. They may think that the vaccine hasn’t worked, but it has likely prevented them from having a more significant infection.
Failure to mount an immune response:
- inappropriate vaccine schedule. Either missed doses, or vaccines given too close together, might mean a full response is not developed
- vaccine factors - no vaccine is 100% effective. Vaccine may not cover the strain that is circulating
- host factors - immunosuppression or older age can mean that a strong immune response is not elicited
Secondary vaccine failure:
- immunity develops initially, then wanes due to older age (immuno-senescence)
