An update of the global burden of pertussis in children younger than 5 years: a modelling study.

BACKGROUND

Since the publication in 2003 of a model to estimate the disease burden of pertussis, new evidence of the protective effect of incomplete pertussis vaccination against severe pertussis has been reported. We revised the model to provide new estimates of regional and global pertussis cases and deaths for children younger than 5 years.

METHODS

We developed a revised model with data from 2014 to estimate pertussis cases and deaths. Pertussis cases were defined according to the WHO clinical case definition, as a coughing illness lasting at least 2 weeks with paroxysms of coughing, inspiratory whooping, or post-tussive vomiting. We used UN population estimates and WHO and UNICEF data on national pertussis immunisation coverage. Estimates were made for vaccine effectiveness against pertussis cases and deaths for one, two, and three doses of vaccination, probability of infection in low and high coverage countries, and case fatality ratios in low and high mortality countries in two age groups: infants younger than 1 year and children aged 1-4 years. We did sensitivity analyses with a range of input parameters to assess the effect of uncertainty of the input parameters on the model outputs.

FINDINGS

We estimated that there were 24·1 million pertussis cases and 160 700 deaths from pertussis in children younger than 5 years in 2014, with the African region contributing the largest proportions (7·8 million [33%] cases and 92 500 [58%] deaths). 5·1 million (21%) estimated pertussis cases and 85 900 (53%) estimated deaths were in infants younger than 1 year. In the sensitivity analyses, the estimated number of cases ranged from 7 million to 40 million and deaths from 38 000 to 670 000.

INTERPRETATION

Our estimates suggest that, compared with the 1999 estimates published in 2003 (30·6 million pertussis cases and 390 000 deaths from pertussis in children younger than 5 years), the numbers of cases and deaths of pertussis have fallen substantially. Model sensitivity emphasised the importance of better surveillance to improve country-level decision making and pertussis control.

FUNDING

None.