Journal Article > Review
Int J Epidemiol. 2009 February 2; Volume 38 (Issue 1); DOI:10.1093/ije/dyn224
Wolfson LJ, Grais RF, Luquero FJ, Birmingham ME, Strebel PM
Int J Epidemiol. 2009 February 2; Volume 38 (Issue 1); DOI:10.1093/ije/dyn224
BACKGROUND: Global deaths from measles have decreased notably in past decades, due to both increases in immunization rates and decreases in measles case fatality ratios (CFRs). While some aspects of the reduction in measles mortality can be monitored through increases in immunization coverage, estimating the level of measles deaths (in absolute terms) is problematic, particularly since incidence-based methods of estimation rely on accurate measures of measles CFRs. These ratios vary widely by geographic and epidemiologic context and even within the same community from year-to-year. METHODS: To understand better the variations in CFRs, we reviewed community-based studies published between 1980 and 2008 reporting age-specific measles CFRs. RESULTS: The results of the search consistently document that measles CFRs are highest in unvaccinated children under age 5 years; in outbreaks; the lowest CFRs occur in vaccinated children regardless of setting. The broad range of case and death definitions, study populations and geography highlight the complexities in extrapolating results for global public health planning. CONCLUSIONS: Values for measles CFRs remain imprecise, resulting in continued uncertainty about the actual toll measles exacts.
Journal Article > ResearchFull Text
Nature. 2008 February 7; Volume 451 (Issue 7179); DOI:10.1038/nature06509
Ferrari MJ, Grais RF, Bharti N, Conlan AJK, Bjørnstad ON, et al.
Nature. 2008 February 7; Volume 451 (Issue 7179); DOI:10.1038/nature06509
Although vaccination has almost eliminated measles in parts of the world, the disease remains a major killer in some high birth rate countries of the Sahel. On the basis of measles dynamics for industrialized countries, high birth rate regions should experience regular annual epidemics. Here, however, we show that measles epidemics in Niger are highly episodic, particularly in the capital Niamey. Models demonstrate that this variability arises from powerful seasonality in transmission-generating high amplitude epidemics-within the chaotic domain of deterministic dynamics. In practice, this leads to frequent stochastic fadeouts, interspersed with irregular, large epidemics. A metapopulation model illustrates how increased vaccine coverage, but still below the local elimination threshold, could lead to increasingly variable major outbreaks in highly seasonally forced contexts. Such erratic dynamics emphasize the importance both of control strategies that address build-up of susceptible individuals and efforts to mitigate the impact of large outbreaks when they occur.