A two-dose schedule for immunization of infants using a more concentrated DPT-vaccine.

In a controlled field-trial in infants in the Philippines, a two-dose schedule with an interval of 6 months between injections using a concentrated adsorbed DPT-vaccine was evaluated. The serologic response against the three components in the vaccine was satisfactory, whereas the side-effects in the concentrated vaccine group did not differ from those observed in a control DPT group. After two injections, the coverage percentage with DPT-vaccine was shown to be higher than 70%. Two implications of the introduction of the two-dose DPT-immunization schedule are discussed, i.e. (a) the possibility of using it as the nucleus of a complete schedule including immunization against poliomyelitis, BCG, smallpox and measles, and (b) the consequences which the interval of 6 months might have on the epidemiological spread of B. pertussis infections.