A1 Refereed original research article in a scientific journal
Sustained reduction in vaccine-type invasive pneumococcal disease despite waning effects of a catch-up campaign in Kilifi, Kenya: A mathematical model based on pre-vaccination data
Authors: Ojal J, Flasche S, Hammitt LL, Akech D, Kiti MC, Kamau T, Adetifa I, Nurhonen M, Scott JAG, Auranen K
Publisher: ELSEVIER SCI LTD
Publication year: 2017
Journal: Vaccine
Journal name in source: VACCINE
Journal acronym: VACCINE
Volume: 35
Issue: 35
First page : 4561
Last page: 4568
Number of pages: 8
ISSN: 0264-410X
DOI: https://doi.org/10.1016/j.vaccine.2017.07.019
Web address : https://www.sciencedirect.com/science/article/pii/S0264410X17309155?via=ihub
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/27628433
Background: In 2011, Kenya introduced the 10-valent pneumococcal conjugate vaccine together with a catch-up campaign for children aged <5 years in Kilifi County. In a post-vaccination surveillance study based in Kilifi, there was a substantial decline in invasive pneumococcal disease (IPD). However, given the continued circulation of the vaccine serotypes, it is possible that vaccine-serotype disease may re-emerge once the effects of the catch-up campaign wear off.Methods: We developed, a compartmental, age-structured dynamic model of pneumococcal carriage and invasive disease for three serotype groups: the 10-valent vaccine serotypes and two groups of non vaccine serotypes based on their susceptibility to mutual competition. The model was calibrated to age- and serotype-specific data on carriage and IPD in the pre-vaccination era and used to predict carriage prevalence and IPD up to ten years post-vaccination in Kilifi. The model was validated against the observed carriage prevalence after vaccine introduction.Results: The model predicts a sustained reduction in vaccine-type pneumococcal carriage prevalence from 33% to 8% in infants and from 30% to 8% in 1-5 year olds over the 10-year period following vaccine introduction. The incidence of IPD is predicted to decline across all age groups resulting in an overall reduction of 56% in the population, corresponding to 10.4 cases per 100,000 per year. The vaccine-type IPD incidence is estimated to decline by 83% while non-vaccine-type IPD incidence is predicted to increase by 52%. The model's predictions of carriage prevalence agrees well with the observed data in the first five years post-vaccination.Conclusion: We predict a sustained and substantial decline in IPD through PCV vaccination and that the current regimen is insufficient to fully eliminate vaccine-serotype circulation in the model. We show that the observed impact is likely to be sustained despite waning effects of the catch-up campaign. (C) 2017 The Author(s). Published by Elsevier Ltd.
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