Abstract and Introduction
A review of worldwide economic evaluations of pertussis booster vaccination for adolescents and adults was conducted. Thirteen cost–effectiveness, cost–utility and economic impact models were identified. The most frequently studied strategies were adolescent booster, one-time adult booster, adult decennial boosters and cocoon strategy. All studies evaluating adolescent booster suggested this was a cost-effective or cost-saving strategy compared with no booster vaccination. Conclusions concerning adult vaccination, alone or in combination with adolescent vaccination, vary between studies. Studies were often strongly affected by assumptions regarding the amount of unreported cases and lack of reliable input data on real incidence, other epidemiological inputs, costs associated with mild disease and herd immunity effects. Reviewed studies were generally in favor of pertussis booster vaccination, but did not identify any optimal vaccination strategy. Future economic evaluations should explore a wider range of strategies, taking into account country-specific considerations.
Pertussis disease is a frequent cause of chronic cough in children, adolescents and adults. While symptoms may be less severe for adults, it is an important public health threat worldwide: estimates from WHO in 2008 suggested that approximately 16 million cases of pertussis occurred worldwide, 95% of which were in developing countries, and that approximately 195,000 children died from this disease. The disease is still a significant cause of morbidity and mortality in infants younger than 2 years of age, and is the leading cause of death in infants younger than 2 months of age in high-income countries.
The childhood formulation DTaP (also known as DTPa or TDaP) combines vaccines against diphtheria, tetanus and pertussis, in which the pertussis component is acellular. In 1991, the US FDA licensed the DTaP vaccine for infants and children. A complete pertussis vaccination schedule includes at least three doses received during the first year of life. A fourth dose of DTaP is sometimes given between 15 and 18 months, and a fifth dose at age 4–6 years.
Where primary and preschool pertussis vaccination has been implemented, there has been a significant reduction in pertussis morbidity and mortality in infants and children.[4–6] However, the disease persists in infants who are too young to be vaccinated, and amongst adolescents and adults who have lost the protection acquired through the disease or the vaccine. Several countries have noted an epidemiological shift in the average age of the onset of pertussis infection, reporting a rising number of cases in adolescents and adults, inducing infection in infants.[4,8,9] For example, the incidence of pertussis notifications in children aged 10–14 years in British Columbia increased from below 50 per 100,000 person-years to approximately 240 per 100,000 between the outbreaks of 1996 and 2000. Moreover, the burden of pertussis disease is likely to be underestimated, due to underconsulting, under-recognition or misdiagnosis, and under-reporting of the disease.
The re-emergence of pertussis disease could potentially be limited by a booster vaccination for adolescents and adults. Many countries (e.g., France, Germany, the USA and Canada) have already integrated a booster for adolescents and/or adults into their current schedule. The Global Pertussis Initiative, set up in 2001 by Sanofi Pasteur, brought together experts from 17 countries that reached consensus on the primary and secondary objectives of various immunization strategies. The universal adult and/or adolescent booster strategies aim at reducing morbidity in vaccinated populations and developing herd immunity, whereas the cocoon booster strategy for selected individuals (parents and childcarers) aims at reducing transmission to infants. The Global Pertussis Initiative recommended universal adolescent immunization and implementation of the cocoon strategy where economically feasible. Universal adult immunization was presented as a "logical goal for the ultimate elimination of pertussis disease". According to the WHO position paper, decisions concerning the addition of booster doses for adolescents and adults should be based on incidence and cost–effectiveness data. In the USA, the Advisory Committee on Immunization Practices recommends a single booster dose (tetanus–diphtheria–acellular pertussis [Tdap]) for persons aged 11–18 years who have completed the recommended childhood DTP/DTaP vaccination series and for adults aged 19–64 years. The Tdap formulation has a reduced dose of diphtheria and pertussis components, substituting the previous Td booster vaccine that combined vaccines against diphtheria and tetanus.
The cost–effectiveness of pertussis booster vaccination has been evaluated in several studies worldwide; however, no review focusing on evaluations of booster vaccination for adolescents and adults has been published to date. The objectives of this article are first to provide a critical literature review of economic evaluations on pertussis booster vaccination, to investigate the disparity of the results among strategies and the reasons for such difference, and to identify those booster vaccination strategies that are likely to be most cost effective. In the context of rising interest in pertussis booster vaccination, it is expected that several economic evaluations will be conducted in the next few years. This review will attempt to provide guidance and suggestions for improvement, as such setting the scene for future economic evaluations.
Expert Rev Pharmacoeconomics Outcomes Res. 2012;12(1):71-94. © 2012 Expert Reviews Ltd.