PhD ceremony Mr. M.H. Rozenbaum: Costs and effectiveness of extended vaccination strategies against pertussis and pneumococcal disease

PhD ceremony: Mr. M.H. Rozenbaum, 11.00 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Costs and effectiveness of extended vaccination strategies against pertussis and pneumococcal disease

Promotor(s): prof. M.J. Postma, prof. E. Hak

Faculty: Mathematics and Natural Sciences

The most important results of the research of Mark Rozenbaum are:

• There are large differences in the observed disease epidemiology after implementation of pediatric pneumococcal immunization programs between the USA and Europe, but also between European countries and even between regions within countries.
• Herd effects reduce the cost-effectiveness of elderly and adult (risk) groups vaccination in time. In particular, a modelling study showed that vaccinating risk groups in England was unlikely to be considered cost-effective in the base-case analysis unless the vaccine would also offer protection against non–bacteraemic pneumonia.
• The observed prevalence of S. pneumoniae in CAP significantly varies between European regions
• The introduction of a pertussis booster dose could reduce the number of hospitalizations among infants less than 4 months of age slightly, while the incidence in adolescents and adults increased.
• An additional pertussis booster dose at the age of 10 years is the most cost–effective booster vaccination strategy. Nevertheless, this strategy only offered limited indirect protection to the (partly) unvaccinated infants with potentially most serious disease which might be a primary aim of extended pertussis vaccination (as do the other booster strategies)

A crowded vaccination schedule and restrained health–care budgets limit the uptake of new vaccines into the Dutch national immunization programs (NIP). Next to many other factors, cost-effectiveness considerations highly influence the decision whether to introduce vaccines into Dutch NIP.

The first part of the thesis of Rozenbaum focuses on the (cost-) effectiveness of pneumococcal vaccination. It is shown that there are large differences in the observed disease epidemiology after implementation of paediatric pneumococcal immunization programs between the USA and Europe. In Europe, less cases of pneumococcal disease were avoided in unvaccinated individuals (herd effects) than in the USA, while significant replacement was observed in Europe with strains not included in the vaccine. As a consequence, the 7-valent pneumococcal vaccine, which was previously used in the Dutch national immunization programme, was less cost-effective as predicted beforehand. More valent pneumococcal vaccines are more likely to be considered cost-effective as more direct and herd effects and less serotype replacement effects are expected. These potential herd effects reduce the cost-effectiveness of elderly and adult (risk) groups vaccination in time. In particular, a modelling study showed that vaccinating risk groups in England was unlikely to be considered cost-effective in the base-case analysis unless the vaccine would also offer protection against non–bacteraemic pneumonia. Evidence on whether the latter occurs is awaited from a large Dutch clinical trial.

The second part of the thesis of Rozenbaum explores the impact of extending the childhood pertussis vaccination programme to adolescents and adults. Given the nature of the problem, the development of a complex population dynamical model was required. The developed dynamic model showed that the most (cost-) effective age for the introduction of an additional booster is around 12 years. Nevertheless, this strategy only offered limited indirect protection to the (partly) unvaccinated infants with potentially most serious disease which might be a primary aim of extended pertussis vaccination.

In conclusion, the dynamics of infectious diseases makes it challenging to predict the impact of new vaccination programs. Extending the vaccination programs against pneumococcal disease and pertussis offers the possibility to prevent morbidity and mortality and decrease the economic burden of disease for society.