Abstract
BackgroundHaemophilus influenzae serotype b (Hib) has yet to be eliminated despite the implementation of routine infant immunization programs. There is no consensus regarding the number of primary vaccine doses and an optimal schedule for the booster dose. We sought to evaluate the effect of a booster dose after receiving the primary series on the long-term disease incidence.MethodsA stochastic model of Hib transmission dynamics was constructed to compare the long-term impact of a booster vaccination and different booster schedules after receiving the primary series on the incidence of carriage and symptomatic disease. We parameterized the model with available estimates for the efficacy of Hib conjugate vaccine and durations of both vaccine-induced and naturally acquired immunity.ResultsWe found that administering a booster dose substantially reduced the population burden of Hib disease compared to the scenario of only receiving the primary series. Comparing the schedules, the incidence of carriage for a 2-year delay (on average) in booster vaccination was comparable or lower than that observed for the scenario of booster dose within 1 year after primary series. The temporal reduction of symptomatic disease was similar in the two booster schedules, suggesting no superiority of one schedule over the other in terms of reducing the incidence of symptomatic disease.ConclusionsThe findings underscore the importance of a booster vaccination for continued decline of Hib incidence. When the primary series provides a high level of protection temporarily, delaying the booster dose (still within the average duration of protection conferred by the primary series) may be beneficial to maintain longer-term protection levels and decelerate the decline of herd immunity in the population.
Highlights
Haemophilus influenzae serotype b (Hib) has yet to be eliminated despite the implementation of routine infant immunization programs
Given the accumulating evidence regarding the role of a primary series plus a booster dose for curtailing Hib disease, we developed a stochastic model of Hib transmission dynamics to evaluate the impact of a booster vaccination with different schedules on the long-term disease incidence in the population
This leads to the rise of herd immunity in the population, which in turn reduces the incidence of infection as observed in the later decline of incidence for both carriage and symptomatic disease
Summary
Haemophilus influenzae serotype b (Hib) has yet to be eliminated despite the implementation of routine infant immunization programs. All Hib vaccines currently licensed for use are conjugated and available as a monovalent vaccine or as a combination vaccine with other antigens [2] The uptake of these vaccines in childhood immunization programs of many countries has increased globally, largely driven by the World Health Organization (WHO) recommendations for primary and booster doses [2]. Data from the United Kingdom suggested that implementing an infant immunization program without a booster dose initially resulted in decreased rates of invasive Hib disease, these rates later increased [13, 14] and the introduction of a booster campaign helped re-establish herd immunity [10]. A recent study in the United States reported that during 2002–2009, more than half of Hib cases occurred among children who were eligible for vaccination but were either behind schedule or completely unvaccinated [17]
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