Parents frequently ask why their children need routine health care when they have already received all of their required immunizations. The answer is simply that Georges Memorial Medical Centre provides an array of diagnostic and preventative services. Infants are checked for growth and developmental delays. At each visit the staff will check the eyes for vision abnormalities and muscle imbalance, the ears for infection, the heart for murmurs, and the hips for developmental dysplasia.

An ideal vaccine should confer long-lasting, preferably lifelong, protection against the disease; it should be inexpensive enough for large scale use, stable enough to remain potent during transportation and storage, and have no adverse effect on the recipient. If the introduction of a vaccine is agreed upon at national level then a further decision has to be made as to whether it should be for general use (e.g. polio vaccine) or for specific use when exposure is possible (e.g. typhoid vaccine, given when travelling to regions where typhoid is endemic).

Vaccines may induce immunity against infection either actively or passively.

Active immunization is brought about by stimulating the individual’s own immunity by introducing either inactivated (killed) or attenuated (live, but enfeebled) agents (Table 2). The protective response by the body is mainly expressed through: (i) specific antibodies, measurable by serological tests, which confer protection against many agents, particularly viruses and toxins. (ii) the cellular immune response, which involves both phagocytes and ‘memory cells’.

Inactivated vaccines are prepared in three ways (examples in Table 2): (i) from killed whole organisms; (ii) from sub-units of the killed organisms; (iii) from the toxins which the organisms release, inactivated by formaldehyde (toxoids).

Passive immunization is obtained by giving pre-formed, antibodies. These are usually injected in the form of human immunoglobulin or, rarely, antisera prepared in animals. Protection is usually rapid, but the immunity derived is often short-lived, being limited to the time taken for the antibodies to be broken down in the body — from a week or so, with animal antisera, to about six months for protection against hepatitis A by human normal immunoglobulin.