Pertussis immunization in the global pertussis initiative North American region: recommended strategies and implementation considerations.

In North America, children currently receive 5 doses of a combined diphtheria-tetanus-acellular pertussis vaccine between the ages of 2 months and 6 years. Although this schedule has reduced the incidence of childhood pertussis, it has not led to the development of herd immunity in the total population, largely because pertussis immunity wanes with time. The time course over which immunity wanes is uncertain; however, high pertussis antibody titers in adolescents and adults indicate unrecognized infection in these groups. There is evidence that this group serves as a source of infection for young infants who are not fully immunized. Therefore, of the potential strategies reviewed by the North American Global Pertussis Initiative group, universal adolescent immunization would in theory reduce the risk of pertussis in this age group and may reduce transmission to young infants. However, because immunity probably wanes at the same rate in adolescents and children, the burden of disease will likely shift to older age groups, including young adults (parents of vulnerable infants). Therefore the ideal would be immunization of adolescents and adults, particularly those who are in contact with young infants. Adolescent immunization is already recommended in Austria, France, Germany and Canada, and participants in the Global Pertussis Initiative recommend that this strategy be implemented across North America with a view to eventually extending immunization to include adults. The final decision to implement such a strategy will depend on pertussis surveillance studies and analysis of the effectiveness and tolerability of adolescent and adult pertussis immunization as well as program considerations related to feasibility and economics.