IMMUNISATION AND IPC Flashcards
Why immunise
Prevent individual disease (life-long, not just in children). Ideally, halt carriage & transmission -> herd immunity is a side effect. Ideally, eliminate > eradicate disease. High coverage is operational target.
Describe at a basic level the immunological concepts underlying active and passive immunisation
Innate immunity: complement, WBC & cytokines
Immune system: immunoglobulin: initially not specific, learns specific IgG response, lays down immune memory
PASSIVE:
Example: Transfer from mother to unborn baby
“Maternal antibodies” can protect the baby for up to a year against illnesses to which the mother is immune.
Example: Immunoglobulin (IG), which contains antibodies pooled together from the blood of many donors, can be injected into a person who needs antibodies. This type of passive immunity, although effective, usually disappears within several weeks or months. Most types of transfused blood contain antibodies.
ACTIVE:
Active immunity is usually long-lasting immunity produced by the immune system in response to antigens. These antigens can be from natural infection or from vaccination. The immune system makes antibodies to help destroy antigens. The benefit of vaccination is that active immunity occurs without disease or disease complications. The persistence of protection for many years after natural infection or vaccination is called “immunologic memory.” Active Immunity can be nature immunity in response to an illness or vaccine induced immunity
Antigen
- An antigen is defined as “anything that can be bound by an antibody“
- Antibodies interact specifically with relatively small parts of molecules. These are known as antigenic determinants or epitopes
Antibody
- Produced to one specific antigen and have variable and constant regions
- Trigger a range of protective effects
- Neutralise toxins/Block adhesion/cell entry/Opsonisation/Kill via complement/ Neutralise viral infectivity and prevents replication
- Different types of antibody: IgM, IgG, IgA, IgE
Primary immune response
develops in the weeks following first exposure to an antigen
- mainly IgM antibody
Secondary immune response
faster and more powerful
- mainly IgG antibody
How do antibodies produce immunity
- Antibodies produced from B Lymphocytes
- Antigen binds non-specifically to variable region of antibody (Ig) molecule. This triggers clonal expansion
- 1st wave of IgM production, followed by IgG production
- IgG binds tightly to antigen and through simultaneous complement binding facilitates the destruction of the antigen-bearing micro-organism
- When infection resolved levels of IgG decline
- However one set of the IgG producing B lymphocytes persist with the ability to recognise that specific antigen = Immunological memory
Vaccination theory – basic concepts
For infections transmitted from person to person, the crucial factor determining the spread of infection is:
How many secondary cases are caused by each infectious person
This is the Susceptible Population
Any person who is not immune to a particular pathogen is said to be susceptible
A person may be susceptible because he / she has not encountered the infection or the vaccine against it before
A person may be susceptible because he / she is unable to mount an immune response
A person may be susceptible because
Live vaccines
Attenuated strains which replicate in host
Attenuation means the virus or bacterium has been weakened to reduce virulence so it cannot cause disease in healthy people
Act like natural infection
Live vaccines are the closest to actual infection and therefore elicit good, strong, long-lasting immune responses
Inactivated vaccines
Either: Suspensions of whole intact killed organisms eg. whole cell pertussis, influenza, rabies, HepA
Or: Acellular and sub-unit vaccines contain one or a few components of organism important in protection eg. acellular pertussis vaccine contains between 2-5 components of the whole cell pertussis bacteria e.g. diphtheria toxoid e.g.Hib polysaccharide
Live vaccines
Advantages
Single dose often sufficient to induce long-lasting immunity
Strong immune response evoked
Local and systemic immunity produced
Disadvantages
Potential to revert to virulence. Contraindicated in immunosuppressed patients. Interference by viruses or vaccines and passive antibody. Poor stability. Potential for contamination
Inactivated / killed vaccines
Advantages Stable Constituents clearly defined Unable to cause the infection Disadvantages Need several doses Local reactions common. Adjuvant needed. Keeps vaccine at injection site. Activates antigen presenting cells. Shorter lasting immunity
Describe the different types of agent available for passive immunisation (pooled products, specific antibodies
Vertical transmission of auto-antibodies from mother to foetus & breastfeeding
Injection of human immunoglobulin
• HNIG – pooled plasma
• Specific – tetanus, botulism, hep B, rabies, varicella
