Timing of immunization against DTP in infants - diphtheria, tetanus and pertussis - Tips from Other

Date: June, 1992

The value of routine immunization against diphtheria, tetanus and pertussis is well established, but disagreement persists as to the optimal timing of immunization in infants. Early immunization has been advocated to provide early protection for the most vulnerable infants and because compliance is thought to be better in younger subjects. The World Health Organization recommends a three-dose regimen beginning at six weeks of age. In many countries, however, immunizations begin when infants are older in order to avoid interference from passively acquired maternal antibodies. In Britain, the immunization schedule was changed from three, five and nine months of age to two, three and four months of age. Booy and colleagues measured antibody responses in infants immunized according to both schedules.

The study included 103 infants immunized during 1988 using the three-, five- and nine-month schedule, and 107 infants immunized during 1990 according to the accelerated schedule. Serum antibodies against diphtheria, tetanus and pertussis were measured before immunization and one month after completion of the immunization course.

All of the infants had satisfactory protective levels of antibodies to tetanus, diphtheria and pertussis. However, significant differences existed between the two groups. The old immunization schedule led to significantly higher antibody concentrations against both tetanus and diphtheria but not against pertussis. In infants immunized using the accelerated schedule, those who had initially high antibodies passively transferred from the maternal circulation did not have optimum production of tetanus and pertussis antibodies.

The authors conclude that although both schedules provide adequate levels of protection, the new accelerated schedule has a significant disadvantage because maternal antibodies inhibit the response to tetanus and pertussis. (Lancet, February 29, 1992, vol. 339, p. 507.)

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