The duration of vaccine-induced immunity is known only by inference. Occasional outbreaks of pertussis have been reported among young adults, particularly health care personnel caring for pediatric populations in which pertussis was prevalent. This information suggests that vaccine-induced immunity is not life-long, but the major morbidity and mortality of pertussis definitely occurs in infants and small children. The disease burden incurred by waning immunity in adults probably is minor.
Benefits from an improved pertussis vaccine are likely to arise from the elimination of adverse side effects rather than from a further decrease in the already reduced disease incidence. Researchers do not expect to produce significant increases in vaccine efficacy, immunogenicity (at lower ages), or utilization. Therefore, no effort has been made to document the current burden of pertussis illness or to calculate what the burden would be in the absence of the current vaccination program, if desired, these calculations could be made with methods devised by Hinman and Koplan (1984).
For this report, the burden of illness that could be eliminated by an improved pertussis vaccine is considered to be equivalent to the adverse effects arising from the current vaccine. The manner in which this has been calculated is described below in the section “Vaccine Preventable Illness.”
The target population for an improved pertussis vaccine would be identical to the target population for the existing vaccine: the entire cohort of infants born every year in the United States. Indeed, simple substitution of an improved pertussis component for the existing whole cell pertussis component in the DPT vaccine would be the desirable goal. This would maintain the present simplicity of immunization patterns for infants and small children. All 50 states have mandatory immunization laws requiring completion of primary immunization prior to school entry.
With an improved, less reactive vaccine it might be possible to offer immunization to older individuals who were, for some reason, not vaccinated. This is not possible with existing vaccines because of adverse reactions with increasing age.
The documented efficacy of the existing pertussis vaccine, when given as recommended, clearly indicates the suitability of pertussis for vaccine control.