Immunization

Immunisation against infectious agents can be achieved either passively, by administration of preformed antibodies, or actively, by the administration of vaccines that induce humoral and/or cell-mediated immune responses. Vaccines in use include live attenuated vaccines such as BCG and MMR, inactivated whole-cell vaccines such as hepatitis A, toxoids such as diphtheria, and subunit vaccines such as hepatitis B. Most vaccines are administered by intramuscular or deep subcutaneous injection, but BCG is given intradermally and certain live vaccines, such as Sabin polio vaccine, are administered orally to induce high-level mucosal immunity. The schedule for routine childhood immunizations, as recommended by the UK Department of Health, includes immunization against diphtheria, tetanus and pertussis, poliomyelitis, Haemophilus influenzae type b, measles, mumps and rubella, BCG and group C meningococcus. Recent concerns over the safety of the MMR vaccine have led to a reduction in its uptake, as occurred with pertussis vaccine in the 1970s, which led to large outbreaks of that infection. Other vaccines are recommended only for selected individuals; these include pneumococcus, influenza, hepatitis B, varicella-zoster virus and hepatitis A. In addition, other vaccines such as rabies, typhoid and yellow fever are recommended only for travellers to certain parts of the world. Vaccines in common use have an excellent safety profile and there are few contraindications. However, live vaccines should not normally be given to immunocompromised individuals. Novel technologies, including genetic approaches, are being applied to develop new vaccines for infections such as HIV and hepatitis C.