Immunisation Case

BTEC NATIONAL CERTIFICATE IN PHARMACEUTICAL SCIENCE

Unit: Action and Use of Drugs C

Area: Immunology - Immunisation

Tutor: Steve Brown / Diane Denman

The principle of immunisation is to increase specific immunity to infection; this may be achieved by the administration of immune serum (passive immunisation) or by administration of an antigen that primes the host immune system without causing disease (active immunisation).

Passive Immunisation

* Passive immunisation means that preformed antibodies (immunoglobulins) of human or animal origin are used to transfer immunity to the host. Since the host's immune system is not involved, this is called passive immunisation.

* The most commonly used preparation is immune globulin, a 25-fold concentration of gamma globulins from human plasma. The normal route of administration is IM or IV.

 Passive immunisation (immunotherapy) gives immediate protection, but immunity lasts for a relatively short time (< 6 months).

 Immunoglobulin for passive immunisation is normally obtained from volunteers (e.g. individuals recently vaccinated) with high titres of specific antibody to a particular organism. However, for infections that are relatively common (e.g. hepatitis A) levels of specific antibody in the general population are high enough to allow the use of pooled plasma from normal blood donors (pooled human immunoglobulin).

 Indications for the use of passive immunisation are limited and include:

(a) post-exposure prophylaxis in immunocompetent hosts when immediate protection is require following exposure to the infection (tetanus, diphtheria, rabies, hepatitis B);

(b) post-exposure prophylaxis in immunocompromised hosts (measles, varicella-zoster);

(c) therapy (e.g. cytomegalovirus (CMV) infection in transplant patients and young children).

*

Active Immunisation

 The underlying principle is to stimulate the production of specific B- and T-lymphocytes (primary response) which develop into memory cells; subsequent exposure to the pathogen then results in the immediate and effective immune response (secondary response)

 Active immunisation provides long lasting protection (often lifelong) against infection, but takes several weeks to become effective.

 Vaccination strategies are:

(a) to protect susceptible individuals against infection;

(b) to reduce the incidence of infection in the community (increase 'herd' immunity);

(c) to eliminate an infection in a particular country or worldwide (e.g. smallpox)

Vaccines

The ideal vaccine should be:

 able to induce an adequate and appropriate immune response without causing active infection;

 safe;

 inexpensive;

 stable;

 easy to administer.

Types of vaccine

Live attenuated

 Live organism whose virulence has been attenuated; this is normally achieved by serial passage in artificial media, e.g. BCG (Bacille Calmette-Guérin) vaccine against tuberculosis; many viral vaccines.

 Advantages: replication of attenuated organism in body closely mimics true infection; generally, only one dose required; inexpensive.

 Complications: random mutations may occur vary rarely, which result in revertence to virulence; cell lines used for virus production may become contaminated with other viruses (strict quality control procedures are necessary).

 Limitations: live vaccines cannot be given to immunocompromised patients or in pregnancy.

Killed organisms

 Organisms killed by chemical or heat treatment, e.g. vaccines against: rabies, influenza, polio (salk vaccine); salmonella typhi, vibro cholera, Bordetella pertussis, yersinia pestis.

 Advantage: can be given to immunocompromised; no revertence to virulence.

 Disadvantage: organism cannot multiply in tissues; several doses required for effective response; expensive.

Toxoids

 Inactivated (formaldehyde treatment) bacterial toxin vaccines e.g. tetanus, diphtheria.

 Disadvantages, relatively small molecules, therefore not immunogenic when given alone; require large molecules (adjuvent) to produce effective immune response.

Subcellular or subviral fractions

 An alternative to using the whole organism is to identify and purify important subunit antigens for use as vaccines.

 Examples include the polysaccharide capsular vaccines for immunisation against pneumococci, meningococci and Haemophilus influenzae type b; hepatitus B; surface antigen, originally purified from the serum of chronic carriers, but now manufactured by recombinant DNA techniques; and influenza haemagglutinin (HA) and neuraminidase (NA) subunit vaccine.

Individual Vaccines

Poliomyelitis

 Both inactivated poliomyelitis vaccine and live attenuated vaccine (oral) are available.

 Incidence of polio drastically reduced in many countries since introduction of routine vaccination, eradication in the Americas attempted for the year 2000.

Measles/Mumps/Rubella (MMR)

 Contains live attenuated measles, mumps and rubella viruses.

 Should be given to children irrespective of history of measles, mumps or rubella.

Influenza

 Vaccine regularly updated to reflect current strains in circulation. Contains two type A and one type B virus strains;