Basic immunization,

Basic immunization strategies and schedules

The decision to immunize at a particular age is, for the most part, a compromise between:

• The desire to immunize as early as possible, thereby protecting the child before he/she becomes exposed to the infectious agent, and
• The requirement to wait both for the infant's immune response to mature and for the maternally-derived antibodies that crossed the placenta pre-natally to disappear, so that the immunization will be effective.

Vaccines are recommended for the youngest age group at risk for developing the disease whose members are known to develop an adequate response to immunization without adverse effects from the vaccine.

The basic schedule calls for all children to receive 1 dose of BCG vaccine, 3 doses of DTP vaccine, 4 doses of OPV, and 1 dose of measles vaccine before their first birthday. In countries where HBsAg carriage rates are >2%, universal infant vaccination with Hep B vaccine is recommended. Where HBsAg carriage rates are lower, adolescent immunization can be considered as an alternative or addition.

Some vaccines require the administration of >1 dose for development of an adequate immune response. The doses should not be given less than 4 wks apart since it may lessen the antibody response. Although increasing the interval will increase the antibody response, the child is then susceptible to infection for a longer time.

As many vaccines as possible should be given in one visit to reduce the number of contacts required.
If a child has missed the EPI schedule, he/she can receive the first dose of all the vaccines that a child of his/her age should have already received, simultaneously. All the EPI vaccines can be safely given at the same time but they should be injected into different sites.

Different vaccines should not be mixed and administered in one syringe.

If vaccines cannot be given on the same day, then live vaccines should be spaced at least 4 weeks apart. A shorter interval may result in interference between the vaccines and a reduction in the immune response.

WHO-recommended infant immunization schedule

Age1 Vaccines Hepatitis B2 Scheme A Scheme B Birth BCG, OPV 0 HB-1 6 weeks DTP-1, OPV-1 HB-2 HB-1 10 weeks DTP-2, OPV-2 HB-2 14 weeks DTP-3, OPV-3 HB-3 HB-3 9 months Measles3 and/or yellow fever 1 . Babies born prematurely should be vaccinated at exactly the same times after birth as babies born at term. 2 . Scheme A is recommended where perinatal transmission of Hep B is common (e.g. S.E. Asia). Scheme B may be used in countries where perinatal transmission is less common (e.g. sub-Saharan Africa). 3 . Where there is a high risk of mortality from measles among children under 9 months (such as hospitalized or HIV-infected infants, or refugee camps), measles vaccination should be carried out at both 6 and 9 months.