A lapse in the immunization schedule does not require reinitiation of entire vaccine series. Immunization should be given at the next visit in the usual doses assuming that the minimum interval has already elapsed and the imunization should be completed at the next available opportunity". D.P.T. and oral polio vaccine which the child already had should be considered as the first dose. The child would need further 2 doses of this vaccine to complete the primary vaccination. Booster doses are administered, once the primary immunization is complete. Thus you cannot administer booster doses of D.P.T. and O.P.V. as their primary immunization is not complete.