Principles of Immunisation

Professor S. Myint

Aims and Objectives

After this session, the student should:

understand the differences between active and passive immunisation
understand the immunological principles behind vaccination
know the general types of vaccine available
know the UK schedule for vaccination
understand the general rules to follow before using vaccines
know the range and basic characteristics of vaccines licensed for use in the UK

Immunisation

Immunisation can be active or passive. Active immunisation is termed vaccination and elicits a response from the body that provides protective immunity. It is long-lasting. Passive immunisation is, in practice, the injection of antibodies to provide short term protection.

Vaccines

Effective vaccines are:

Safe
Protective for sustained period
Induce neutralising antibody

In addition they should be:

Biologically stable
Cheap to produce
Easy to administer

Currently available vaccines are either:

Live (attenuated)
Killed
Fractionated
Recombinant

Immunological Principles of Vaccination

Vaccination is intended to provide long-term protection after its administration. Effector T- and B-cells last only a few days, so the prime requisite of any vaccine is to generate immunological memory. Successful vaccines:

activate antigen-presenting cells to initiate antigen processing and produce cytokines
activate both T and B cells to give a high yield of memory cells
generate Th and Tc cells to several epitopes, to overcome the variation in the immune response in the population due to MHC polymorphism
enable the persistence of antigen, probably on follicular dendritic cells in lymphoid tissue, to elicit continued production of antibody from B cells.

Whole organism vaccines tend to have these abilities. Subunit vaccines can be enhanced to produce these results by the use of adjuvants, such as alum.

UK Schedule of Vaccination

Age	Vaccine
2/3/4 months	Diphtheria/tetanus/pertussis and poliomyelitis (each month) and Haemophilus influenzae b (one dose)
12-18 months	Mumps/Measles/Rubella (MMR)
4-5 years	Booster diphtheria/tetanus and poliomyelitis
10-14 years	BCG
15-18 years	Booster tetanus and poliomyelitis

Licensed Vaccines

Vaccine	Type	Notes
Diphtheria	Toxoid	Schick test to check immunity
Tetanus	Toxoid
Pertussis	Killed Bordetella pertussis	Vaccination should be deferred if there is an acute neurological condition
Poliomyelitis	Live, attenuated	Oral. Killed parenteral vaccine also available.
Haemophilus influenzae b (Hib)	Conjugate capsular polysaccharide	Can also be used in outbreaks
MMR	Live, attenuated	Side effects occur due to individual virus components
BCG	Live attenuated M. bovis	Less effective in endemic areas
Influenza	Disrupted virus or subunit	Triple vaccine containing strains circulating in that year
Pneumococcus	Capsular polysacharide	Polyvalent with 23 capsular types
Hepatitis A	Inactivated
Hepatitis B	Recombinant HBsAg
Rabies	Inactivated	Used post-exposure usually
Cholera	Inactivated Inaba and Ogawa serotypes
Typhoid	Inactivated or capsular polysaccharide (Vi) or live attenuated (TY21a)
Yellow fever	Live, attenuated
Meningococcus	Polysaccharide	Only effective against types A and C
Japanese encephalitis B	Inactivated	For travellers to Far East
Tick-borne encephalitis	Inactivated	For travellers to forested areas
Anthrax	Antigen
Vaccinia	Live attenuated
Varicella-zoster virus	Live attenuated

Principles of Administration and Adverse Effects

In clinical practice, the administrator of any vaccine should check with the manufacturers' instructions before administration. Further details are available in the handbook `Immunisation against Infectious Disease' published by HMSO.