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Dengue has emerged in the past two decades as a rapidly growing and widespread public health problem, with over half of the world's countries and people now at risk.1 In new estimates from the Global Burden of Disease study published in The Lancet Infectious Diseases, Jeffrey Stanaway and colleagues2 suggest that dengue incidence has increased six-fold from 1990 to 2013, accompanied by much flatter mortality trends. Dengue is still regarded as a neglected disease,3 yet its incidence is increasing at an alarming rate, by contrast with declines in other neglected diseases.4 WHO estimates that 50 million to 100 million cases occur annually.5 In 2012, however, formal modelling put the number of dengue infections as high as 390 million (95% credible interval 284 million-528 million), but included both inapparent and apparent cases.1 Their estimated number of apparent cases (96 million, 95% credible interval 67 million-136 million) lies at the high end of the WHO estimates.
Against this background, these new estimates from the Global Burden of Disease Study suggest a much lower number of cases for 2013: 58·4 million (95% uncertainty interval 23·6 million-121·9 million).2 Why is it so difficult to arrive at consistent estimates? Poor disease surveillance, low levels of reporting, lack of inexpensive point-of-care diagnostic tests, and inconsistent comparative analyses are the main reasons, in common with other diseases in low-income and middle-income countries. As good as modelling methods may be, outputs are inevitably compromised by scanty and poor quality data inputs, and they have no means of external validation.6 In the case of dengue, difficulties are further compounded by cyclical epidemics with major troughs and peaks that might be difficult to model. It is of concern that despite applying large expansion factors, the authors' estimates of dengue incidence in the ten countries where recent dengue vaccine trials have been done were consistently lower than...