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Clin Infect Dis. 2018 Oct 13. doi: 10.1093/cid/ciy875. [Epub ahead of print]

Differences in the impact of pneumococcal serotype replacement in individuals with and without underlying medical conditions.

Author information

Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT, USA.
Department of Biostatistics, Yale School of Public Health, New Haven, CT, USA.
Department of Bacteria, Parasites and Fungi, Statens Serum Institut, Copenhagen, Denmark.
Department of Pediatrics, Yale School of Medicine, New Haven, CT, USA.
Infectious Disease Epidemiology & Prevention, Statens Serum Institut.
Department of Infectious Diseases and Pulmonary Medicine, Nordsjaellands Hospital, Copenhagen University Hospital, Denmark.



Pneumococcal conjugate vaccines (PCVs) have had a well-documented impact on the incidence of invasive pneumococcal disease (IPD). However, declines in IPD due to vaccine-targeted serotypes have been partially offset by increases in IPD due to non-vaccine serotypes (NVT). 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.


We used nationwide surveillance data for IPD 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 co-morbidities. Differences in the magnitude of serotype replacement were due to variations in the incidence of NVT in the different risk groups before the introduction of PCVs. The relative increases in the incidence of IPD caused by specific NVTs did not differ appreciably between risk groups in the post-vaccination period. Serotype replacement offset a greater proportion of the benefit of PCVs in strata in which the NVT comprised a larger proportion of cases prior to the introduction of the vaccines. These findings could help to predict the impact of next-generation PCVs in specific risk groups.


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