A vaccine is a biological substance aides in the specific protection of our body against a given disease. A vaccine can be used to stimulate the production of protective antibodies thereby alerting the body systems. A variety of vaccines are available in the market. Almost all killer diseases are successfully controlled by using vaccines. Depending upon how we obtain the vaccines, they classified into many types such as live attenuated, inactivated or killed, cellular fractions, toxoids or combination of these. More recent preparations are sub-unit vaccines and recombinant vaccines. Let us discuss each one in detail.
Live vaccines are prepared from live organisms, for example, BCG, measles, oral polio; they’re otherwise known as live attenuated vaccines. These organisms are subjected to repeated tissue culture in the laboratory sot hat they lost their capacity to induce full-blown disease, however, they retain their ability to immunize. Live vaccines are more potent immunizing agents than killed vaccines, because of the following reasons
Live organisms multiply in the host where the resulting antigenic dose is larger than what is injected.
Live vaccines have all the major and minor antigenic components.
Live vaccines engage certain tissues of the body while producing immunity. For example, the intestinal mucosa is involved by the oral polio vaccine.
Indications and contraindications of live vaccines
Live vaccines should never be administered to those individuals with immune deficiency diseases or to persons whose immune response was suppressed due to blood cancer, tumours, or lymphoma.
Persons receiving corticosteroids, alkylating agents, metabolic agents, or radiation are also exempted from receiving live vaccines.
Pregnancy is another contraindication. However, if the benefits exceed the risk after injecting, we need to estimate it beforehand and then inject it only if necessary.
Tips for Administration of live vaccines
When 2 different live vaccines are required, they should be given either simultaneously at different sites or with an interval of at least 3 weeks. In the case of live vaccines, immunization is generally achieved with a single dose. The exception is the polio vaccine as it needs three or more doses to be given at spaced intervals to produce the desired level of immunity. Live vaccines usually produce long-term immunity, but not as long as that of the immunity triggered by natural infection. Live vaccines must be properly stored to retain their effectiveness. Serious failures of measles and polio immunization have resulted from inadequate refrigeration prior to use.
Inactivated or killed vaccines
Organisms killed by heat or chemicals, when infected into the body stimulate active immunity. They are usually safe but less effective than live vaccines. For example, cholera vaccine offers only 50 per cent protection. The efficacy of 3 doses of pertussis vaccine is about 80 per cent in the first three years, and almost "nil" 12 years after immunization. Killed vaccines usually require the main series of 2 or 3 doses of vaccine to produce an adequate antibody response, and in most cases, "booster" injections are required. The duration of immunity following the use of inactivated vaccines varies from months to many years. Inactivated polio vaccine has been quite an effective vaccine, the widespread use of which in certain countries has led to the elimination of the disease. Killed vaccines are usually administered by subcutaneous or intramuscular route. The only absolute contraindication to their administration is a severe local or general reaction to a previous dose.
Vaccines, in certain instances, are prepared from extracted cellular fractions, e.g, meningococcal vaccine from the polysaccharide antigen of the cell wall, the pneumococcal vaccine from the polysaccharide contained in the capsule of the organism and hepatitis B polypeptide vaccines. Although the duration of experience with these vaccines is limited, their efficacy and safety appear to be high.
If more than one kind of immunizing agent is included in the vaccine, it is called a mixed or combined vaccine. The aim of combined vaccines is to simplify administration, reduce costs and minimize the number of contacts of the patient with the health system. The following are some of the well-known combinations:
DPT (Diphtheria pertussis-tetanus)
DPT and typhoid vaccine
MMR (Measles, mumps and rubella)
DPTP (DPT plus inactivated polio)
Hepatitis A, and B
Hepatitis A, and typhoid.
Certain organisms produce exotoxins, e.g., diphtheria and tetanus bacilli. The toxins produced by these organisms are detoxicated and used in the preparation of vaccines. In general, toxoid preparations are highly efficacious and safe immunizing agents. In a toxin, the vulnerability to disease is suppressed while increasing the potency of it. TT( tetanus toxoid) is the most commonly used toxoid.
The term polyvalent is referred to vaccines such as polio and influenza as they are prepared from 2 or more strains of the same species. The term auto or autogenous vaccine is used when the organism in the vaccine is obtained from the same patient. Some vaccines are presented as plain vaccines, but a few as supplementary. Plain vaccines are less efficacious than adjuvant vaccines. Adjuvants are substances that are added to vaccines with the aim to trigger the immune response so that a greater amount of antibodies are produced, and a lesser quantity of antigen is required with fewer doses to be given.