Vaccines

VACCINES

Vaccines are antigenic materials consisting of the whole microorganism or one of its products. Vaccines are of 3 types:

Killed (Inactivated) Vaccines: consist of microorganisms killed by heat or chemicals.

Live Attenuated Vaccines: consist of live bacteria or viruses which have been rendered avirulent. They nevertheless grow and multiply in the body of the host to a limited extent. In individuals with impaired host defence, e.g.

·            Leukaemia or other malignancies, especially those receiving cytotoxic  chemotherapy.                            

·            Systemic lupus erythematosus.

·            Corticosteroid recipients.

·            AIDS and other immune deficiency states. 

The limited virulence of organisms in the live vaccine may be sufficient to cause a disease; live  vaccines are contraindicated in them.

Two live vaccines, if not given together, should preferably be administered with a gap of 1 month.

Toxoids: are modified bacterial exotoxins so that toxicity is lost but antigenicity is retained. The term ‘vaccine’ is sometimes restricted to preparations of whole microorganisms and toxoids are enumerated separately.

Active immunization with vaccines may fail to ‘take’ during corticosteroid or immunosuppressant medication and should be avoided. Vaccination should be deferred in the presence of any acute (especially respiratory) infection and during pregnancy. Antibiotics added during production of vaccines and present in trace amounts in viral vaccines may cause reaction in individuals sensitive to these. Egg proteins (in vaccines prepared on chick embryo) and other materials used for vaccine culture may be responsible for allergic reactions. Adrenaline injection (1 in 1000) should be available to control allergic reaction to the vaccine, if it occurs.

The antibodies developed in response to live or killed vaccines inactivate the bacteria/virus when it subsequently enters the body, while those induced by toxoids neutralize the elaborated exotoxin. The latent period between vaccination and development of immunity and the period for which it lasts depends primarily on the organism, but varies somewhat in different individuals. Viral vaccines and toxoids generally afford more prolonged protection than bacterial vaccines. The important vaccines are described briefly.