Estimating the Population-Level Effectiveness of Vaccination Programs in the Netherlands.

BACKGROUND

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.

METHODS

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 noncommunicable infectious disease for which only direct effects are anticipated. Mortality data from 1903 to 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 prevaccination 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.

RESULTS

Each vaccination program showed a high overall effectiveness, increasing to nearly 100% within 10 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.

CONCLUSION

Vaccination programs for diphtheria and pertussis showed substantial indirect effects, providing evidence for herd protection.