PCL8- IMMUNISATION

PREPARE AN UMBRELLA BEFORE IT RAINS, READY A BOAT BEFORE IT FLOODS

- Malay Idiom


INTRODUCTION
- World Bank notes- vaccines most cost effective health interventions

- Gives control over disease-related morbidity and mortility

- Not risk free- risk to individual must always be balanced with benefits
and population at large

- Sustained vaccination programmes for each birth cohort will continue to be necessary
to control vaccine preventable infection unless their etiological agents can be
eradicated from around the world.

- Major fatal and disabling disease of childhood are rarely seen today, - the risk of
immunisation be perceived to outweigh the benefits.




IMPACT OF IMMUNISATION
- Eradication of small pox, naturally transmitted poliomyetis.



PRINCIPLES OF IMMUNISATION
- Immune system is geared toward the recognition of and response antigens.

- Vaccines convey antigen to elicit immune responses that are generally protective.

- Immune response in the form of antibodies, or activated immune cells that recognise
particular antigens.

- Active immunisation (long-lasting) or passive (adminstration of exogenously produced
immune substance). Combination can cause complementary effect or interfere with
development of immunity.

- All individual cannot be expected to respond identically because immune response is
genetically control.

- Whole organism vaccine may contain all protective antigens but theres more risk of
adverse response to reactive but nonprotective antigens in the mix.



APPROACHES TO ACTIVE IMMUNISATION

- Two standard approache to active immunisation
1. use of live attenuated infectious agents
2. use of inactivated agents, their constituents, or products

- For many disease both live and and inactivated vaccine have been employed each with
advantages and disadvantages.

- Life-attenuated
1. Consist of selected or genetically altered organism that are avirulent of
dramaticallly attenuated, yet immunogenic
2. Caused subclinical or mild illness and immune response that mimics natural
infection.
3. Advantage of microbial infection in vivo, stimulates natural infection: may confer
life-long protection, present all potential antigens, including those only made in
vivo, - hence overcoming immunogenetic restirctions in some host and reach local
sites relevant to induction to protective immunity.

- Inactivated agents
1. Typically require multiple doses and periodic boosters, except polysacchiride
vaccines.
2. Admistered parenterally failed to produce mucosal immunity- because lack delivery
system that can affectively transport them to mucosal antigen-processing cells.
3. Still can be very efficacious, e.g. hepatitis A vaccine.
4. Form available
~ inactivated whole organism
~ detoxified protein exotoxins
~ recombinant protein antigens
~ carbohydrate antigen

- Inactivated vs Live
1. Eventhough live has many advantages, -not always preferable.
2. Live may confer rare but real risk- e.g. in live oral polio vaccine due to
reversion of virulence.


APPROACHES TO PASSIVE IMMUNISATION

- Provide temporary immunity in a person exposed infectious disease and has not been
actively immunised- can arise when active immunisation is unavailable or simply has
not been implemented.

- Used in certain illness associated with toxins, and snake and spider bites and
specific or nonspecific immunosuppressant

-Three types of preparations can be used
1. standard human serum globulin
2. special immune serum globulin with known content of antibody
3. specific animal antisera and antitoxins


ROUTES OF ADMINSTRATION

- Adminstration takes routes of infections, patterns of transmission and predispositions
for certain age groups as factors to maximise protection and minimise adverse affects.

- Guided by immunologis principles and shaped by slinical trials.

- Each vaccine has unique characteristics adapted to a particular route and must be
given by the license route for which it has optimum affect and safety.



AGE

- Age influences response to vaccines- schedules for immunisation are based on age-
dependent responses determined empirically in clinical trials. e.g. presence of
maternal antibody and immune maturity.



TARGET POPULATION AND TIMING OF ADMINSTRATION

-Disease attack rates differ and timing of immunization must consider these variation
along with
1. age specific response to vaccines.
2. durability of immune response
3. logistics optimal identification and vaccination of the groups at risk

- Demographic parameters- as much community as individual endeavours.



ADJUVANTS

- The immune response to some antigens is enhances by the addition of adjuvants-
nonspecific boosters of immune response.

- Essential to efficiacy of certain inactivated vassines including diphtheria and
tetanus toxoids.

- The mechanism is not well defined, but it apperas to relate to the ability of the
adjuvant to activate antigen presenting cells/

- Render soluble antigens into a particulate form, mobilization of phagocytes, and
slowing down antigen release.

- High priority in dicovery of new adjuvats that are safe, more effective, and
inexpensive.


SOURCE: Keusch G, Bart K, Miller M, Harrison's Principls of Internal Medicine 17th ed., Chapter 116: Immunisation Principles and Vaccines Use, McGraw Hill Companies Inc. 2010