Identifying drivers of pertussis disease resurgence pilot study: Final report

Three separate transmission models were developed to investigate the drivers of pertussis resurgence in the United States (US), United Kingdom (UK) and Australia. While these models were all able to reproduce pertussis trends in the setting for which they were developed, they include different assumptions about infection, immunity and vaccination, reflecting the uncertainties of pertussis epidemiology. A key question is whether, despite these differences, these models produce consistent results across settings with diverse vaccination schedules, epidemiologic histories and surveillance systems. A pilot study was conducted in 2016 for the World Health Organization to examine whether findings from the US, UK and Australian models were generalisable to other country contexts. In Stage I of the study, each of the UK, US and Australian models was applied to the other two settings, using the previously identified best fitting parameter sets. The major aim of this phase was to determine whether there is overall evidence that the models may be applied to high-income countries with long histories of pertussis vaccination. In Stage II of the study, each of the UK, US and Australian models was fitted to the other two settings using the same model selection techniques originally applied, to evaluate consistency of model results and identify broadly congruent characteristics of pertussis transmission and immunity. A major aim of this phase was to determine whether, for a given country, the different models provided similar reasons for pertussis resurgence. Each of the models worked well in the setting for which they were designed, but were not able to capture all of the epidemiologic features in different countries. Limited availability of historical data on vaccination, age-specific burden of disease and the relationship between infection and disease is likely to make fitting of the models to other settings without adaptation challenging.