There are few estimates of the effectiveness of long-standing vaccination programs in developed countries. To fill this gap, we investigate the direct and indirect effectiveness of childhood vaccination programs on mortality at the population level in the Netherlands.
We focused on three communicable infectious diseases, diphtheria, pertussis, and poliomyelitis, for which we expect both direct and indirect effects. As a negative control, we used tetanus, a non-communicable infectious disease for which only direct effects are anticipated. Mortality data from 1903–2012 were obtained from Statistics Netherlands. Vaccination coverage data were obtained from various official reports. For the birth cohorts 1903 through 1975, all-cause and cause-specific childhood mortality burden was estimated using restricted mean lifetime survival methods, and a model was used to describe the pre-vaccination decline in burden. By projecting model results into the vaccination era, we obtained the expected burden without vaccination. Program effectiveness was estimated as the difference between observed and expected mortality burden.
Each vaccination program showed a high overall effectiveness, increasing to nearly 100% within ten birth cohorts. For diphtheria, 14.9% (95% uncertainty interval [UI]: 12.3%, 17.6%) of mortality burden averted by vaccination was due to indirect protection. For pertussis, this was 32.1% (95% UI: 31.3%, 32.8%). No indirect effects were observed for poliomyelitis or tetanus with -2.4% (UI: -16.7%, 7.1%) and 0.6% (UI: -17.9%, 10.7%) respectively.
Vaccination programs for diphtheria and pertussis showed substantial indirect effects, providing evidence for herd protection.
Contributors: MvW obtained, extracted, and analyzed the data, searched the scientific literature, and wrote the first draft of the manuscript. MvW, SAM, HEdM, MJP, and JW designed the study and revised the manuscript. MJP and JW conceived the project.
Conflict of interests: MJP received grants and honoraria from various pharmaceutical companies, including GlaxoSmithKline, Pfizer, and Sanofi Pasteur MSD, who are potentially interested in the subject matter of this Article.
Source of Funding: This work was supported by the Dutch Ministry of Health, Welfare and Sport.
Code and data: The data are not yet available for replication, because they will be made publically available through the Dutch National Institute for Public Health and the Environment at a later date. Code used in the analysis is available upon request.
Acknowledgments: We thank Statistics Netherlands for providing access to the data used in this study.
Corresponding author: Maarten van Wijhe, PO Box 1, 3720 BA Bilthoven, The Netherlands, Tel: + 31 6 4566 1018, e-mail: email@example.com
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