Thanks to widespread vaccination, measles outbreaks are currently rare in industrialized countries such as the USA. But measles still kills hundreds of thousands of children each year in developing countries, where vaccination is still patchy. The situation is particularly bad in sub-Saharan Africa, where roughly half of all measles-related deaths now occur.
A team that included Matt Ferrari, Ottar Bjornstad, Bryan Grenfell and collaborators from Medicins San Frontieres and the Niger Ministry of Health is investigating the pattern of measles epidemics in Niger, where around 40,000 cases are reported each year.
The researchers examined data from a measles outbreak in the capital city, Niamey, and found that RE — the number of secondary cases arising from an initial case — is much lower than in industrialized countries at equivalent vaccination levels.
This is not surprising, given that population age structures, spatial distributions and temporal movement patterns (including seasonal migrations) all differ. However, as the researchers point out, it demonstrates that any mathematical models used to recommend vaccination strategies need to be based on relevant data. In particular, if RE is low and spatial movement of populations limited, it may be practicable to use vaccination to limit epidemics within cities, even once an epidemic has taken off. Hitherto, models based on data from industrialized countries have predicted that intervention within urban areas would not be effective once an epidemic was underway.
Written By: Grais RF, Ferrari MJ, Dubray C, Bjornstad ON, Grenfell BT, Djibo A, Fermon F, & Guerin PJ
Journal: 100: 867-873
Journal Reference: 100: 867-873