Prescribing Notes

Immunisation

Immunoglobulins for passive immunisation can be divided into two classes. Normal immunoglobulin is prepared from pooled human plasma and used for protection against measles and, in limited cases, hepatitis A. It has also been used to protect against rubella in susceptible pregnant women, as long-term replacement therapy for congenital agammaglobulinaemia and for idiopathic thrombocytopenic purpura not responding to conventional treatment. It is usually given im, but iv preparations are available for patients receiving long-term therapy who cannot be given repeated i.m. injections. Specific immunoglobulins are prepared from immunised donors or convalescent patients. They are used against particular diseases such as hepatitis B, tetanus, varicella zoster and rabies and also to prevent sensitisation to Rh antigen. Protection with both types of immunoglobulin is immediate but short lasting (2 to 3 months).

Vaccines for the induction of active immunity are of three main types. Live vaccines contain an attenuated strain of the micro-organism intended to cause a subclinical infection. Some vaccines, notably measles vaccine, may cause a mild febrile illness. Killed micro-organisms provide a second type of vaccine. It may either be the intact organism (eg, hepatitis A, typhoid, pertussis, or rabies) or specific antigens, as in the case of influenza and hepatitis B (virus surface antigens). Bacterial toxins (toxoid vaccines) which have been inactivated are also used in vaccine preparations. Tetanus and diphtheria are two examples. There is a special preparation of diphtheria toxoid for adults, who may experience unpleasant side-effects from the preparation used for childhood immunisation. Viral vaccines, both attenuated strains and inactivated virus, are prepared in tissue culture which may contain antibiotics, or in chick embryos. They are therefore contraindicated in patients allergic to the antibiotics concerned (see SPCs) or to egg protein.

mRNA vaccines are a newer type of vaccine which work by introducing the mRNA encoding a viral antigen into the body, so the person's own cells produce the antigen that generates the immune response. In a different but related approach, modified forms of certain viruses (eg, adenovirus) can also be used as vectors to deliver the gene for the viral antigen into the body.

Onset of protection with active immunisation is slower than passive immunisation but lasts for many years, or even for life.