Immunization schedule for children

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Immunological agents include products for both – active immunization i.e. vaccines, as well as passive immunization i.e. immunoglobulins.

Vaccines are formulations containing live or killed pathogens, their subunits or their toxins, minus their virulence. Currently available immunization schedule for children Vaccines may be classified into different types based upon the viability of organisms, contents and the methods of production. Some commonly used terms in vaccine technology are as follows

Live vaccines are highly immunogenic but require stringent storage conditions to maintain viability of organisms and cannot be used in severely immuno deficient children due to the risk of disseminated disease. These vaccines are usually supplied in lyophilized form to increase their stability and have to be reconstituted before use.

Inactivated or toxoid vaccines are less immunogenic but relatively heat-stable and can be used in immune compromised children. Polysaccharide vaccines use a specific component of the organism e.g. polysaccharides antigens from cell wall or capsule.

However, as polysaccharides are poor antigens, these vaccines are usually ineffective in younger children before 2 years of age.

Conjugated vaccines are modified polysaccharide vaccines in which component polysaccharides are conjugated with some other potent antigen, termed as vehicle (e.g. mutant diphtheria or tetanus toxoid), to increase the immunogenicity. These conjugated vaccines can be used in children < 2 years of age, despite being polysaccharide vaccines.

Polyvalent vaccines for immunization schedule for children are the vaccines with two or more strains of the same organism e.g. OPV.

Combination vaccines are vaccines containing antigenic material from different organisms e.g. DPT, DT, MMR and others. These vaccines are useful to minimize the hospital visits, cost and number of pricks.

In addition to the basic antigenic material, vaccines may also contain other agents e.g. adjuvants, preservatives and need diluents.

Adjuvants e.g. aluminium hydroxide or phosphate etc., are added to augment the potency of vaccines, by prolonged release of antigen and the attraction of inununocompetent cells around the injection site.

Preservatives e.g. mercurial compounds or antibiotics e.g. neomycin, are added to prevent contamination of vaccines. These agents have been implicated in various adverse events of vaccines, earlier considered due to antigen component.

Measles vaccine does not contain any preservative and hence, severe septic reactions e.g. toxic-shock syndrome have been reported with its use beyond 3 hours of reconstitution.

Immunization schedule for children

Number of essential vaccines for routine immunization vary from country to country and need to be revised time to time, depending on the local disease prevalence, epidemiological features e.g. common age of infection, availability of safe and effective vaccine, economic feasibility and cost-effectiveness, and logistic considerations.

An appropriate immunization schedule considers that —

• Immunization should be completed as early as possible, as VPDs mostly occur in younger children.

• Different vaccines need to be given at different and appropriate ages – many vaccines e.g. DPT or measles do not induce satisfactory seroconversion if given before 6 weeks or 6 months respectively due to interference by transplacental antibodies.

Similarly, polysaccharide vaccines e.g. Typhoid or Pneumococcal vaccines are weakly immunogenic and not effective before 2 years of age. On the other hand, vaccines inducing cell mediated or local immunity (BCG and OPV respectively) may be given at birth.

• Immunization schedule for children should be completed in minimum number of visits, to avoid inconvenience to parents and drop-outs.



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