Vaccines are used to promote active immunity. They may be administered by different routes; mostly they are given orally or parenterally. Passive immunity can be provided for short term protection or disease management by the use of specific immunoglobulins (eg. hepatitis A, tetanus).
Vaccines may contain inactivated or attenuated live organisms, their subunits or toxins. Inactivated vaccines produce their protective effect by stimulating the production of antibodies; live attenuated vaccines induce the production of both protective antibody and cell mediated immunity.
In general, inactivated vaccines (eg. pertussis, hepatitis A) require a series of doses before inducing long term immunity whereas live vaccines (eg. measles, mumps and rubella) induce long term immunity in more than 90% of recipients after a single dose.
There is a number of combined (polyvalent) vaccines. For example:
New technologies are being used to develop a whole new range of combined vaccines and single dose slow release vaccines. Hepatitis B was the first vaccine to be prepared by recombinant DNA technology. Other recombinant vaccines are being developed using live vectors. Experimental work is now focusing on the use of naked DNA for vaccines. In theory, the ideal vaccine is stable, safe, administered orally in a single dose at birth, 100% effective, reasonably priced and protective for a lifetime.
When planning a vaccination program in a particular community, the benefits that are likely to occur depend upon the severity of the disease in the population, the efficacy of the vaccine and the vaccination rate required to contain, eliminate or eradicate the infection. Programs may be targeted at risk groups in the population (eg. hepatitis A) or may aim to include the whole population (eg. tetanus, diphtheria). In general, infants respond less well immunologically to vaccines than older children and adults and therefore require earlier booster doses of vaccines.
Schedules will change and become simpler when new multivalent vaccines become available. Immunisation of pregnant women in developing countries to prevent tetanus in the neonate is the first example of the trend towards commencing immunisation early when it is technically possible.
Cost benefits of any program must always be considered. The cost benefits of the vaccines presently included in the routine infant schedule are very high (about $14 saved for every $1 spent in USA).
Before vaccines are approved for general use they are tested for safety and effectiveness in clinical trials. The vaccines used in the routine infant schedule are exceptionally safe and effective.However no vaccine is 100% safe or 100% effective. Adverse neurological sequelae are the reactions thatare likely to be of most concern. In Australia we have an Adverse Events Reporting Scheme to monitor these extremely rare occurrences.
Most vaccine preventable diseases are sufficiently serious to be mandatorily notifiable in Australia. It is particularly important to have good incident data both prior to, and after, the introduction of vaccination programs, to monitor the effects of the programs and to detect problems such as poor compliance or ineffective vaccine batches.
Even so, most notifiable conditions are significantly under-reported and other methods of surveillance are also incomplete.
Ada GL. The immunological principles of vaccination. Lancet 1990; 335(8688): 523-525
Burgess, M., Forrest, J. & Jones, C.A., Congenital Rubella Surveillance data summary 2002-3.
Burgess MA. Strategies for measles-mumps-rubella vaccination. In: Hall R, Richters J, eds. Immunisation: the old and the new.
Proceedings of the second national immunisation conference. Canberra: Public Health Association of Australia Inc, 1992; 8890
Gardner, Pierce, Schaffner W. Current concepts: Immunization of adults. New Engl J Med 1993; 328(17):1252-1258.
The chapter Rubella in Harrison's Principles of Internal Medicine. New York: McGraw-Hill, Medical Pub. Division, c2005.
NHMRC. The Australian Immunisation Handbook (9th Edition 2008)
Peter G. Childhood imrnunizations. New Engl J Med 1992; 327(5): 1794-1800.
Immunisation Provider Guidelines. National Varicella (chickenpox) Vaccination Program