ABSTRACT
Background Pneumococcal conjugate vaccines (PCVs) have had a well-documented impact on the incidence of invasive pneumococcal disease (IPD) worldwide. However, declines in IPD due to vaccine-targeted serotypes have been partially offset by increases in IPD due to non-vaccine serotypes. The goal of this study was to quantify serotype-specific changes in the incidence of IPD that occurred in different age groups, with or without certain co-morbidities, following the introduction of PCV7 and PCV13 in the childhood vaccination program in Denmark.
Methods We used nationwide surveillance data for IPD in Denmark and a hierarchical Bayesian regression framework to estimate changes in the incidence of IPD associated with the introduction of PCV7 (2007) and PCV13 (2010) while controlling for serotype-specific epidemic cycles and unrelated secular trends.
Results and Conclusions Following the introduction of PCV7 and 13 in children, the net impact of serotype replacement varied considerably by age group and the presence of comorbid conditions. Serotype replacement offset a greater fraction of the decline in vaccine-targeted serotypes following the introduction of PCV7 compared with the period following the introduction of PCV13. Differences in the magnitude of serotype replacement were due to variations in the incidence of non-vaccine serotypes in the different risk groups before the introduction of PCV7 and PCV13. The relative increases in the incidence of IPD caused by non-vaccine serotypes did not differ appreciably in the post-vaccination period. Serotype replacement offset a greater proportion of the benefit of PCVs in strata in which the non-vaccine serotypes comprised a larger proportion of cases prior to the introduction of the vaccines. These findings could help to predict the impact of next-generation conjugate vaccines in specific risk groups.
Acknowledgements
This work was funded by NIH/NIAID grants R01AI123208 and R56AI110449 to DMW. Support was also received from the Bill and Melinda Gates Foundation (OPP1176267 and OPP1114733), the National Institute on Aging Grant #P30AG021342 (Scholar at the Claude D. Pepper Older Americans Independence Center at Yale University School of Medicine) and from grants # UL1TR001863, UL1 TR000142 and KL2 TR000140 from the National Center for Advancing Translational Science (NCATS), components of the National Institutes of Health (NIH), and NIH roadmap for Medical Research. The findings and conclusions of this paper are those of the authors and do not necessarily represent the official position of the NIH or the Statens Serum Institut.
Footnotes
Declaration of interests: DMW and ZBH have received travel grants and consultancy fees from Pfizer, GSK. DMW and ZBH have received support from the Robert Austrian Research Award in Pneumococcal Vaccinology, which is supported by Pfizer. The other authors declare no conflicts.