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PLoS Comput Biol. 2017 Apr 4;13(4):e1005474. doi: 10.1371/journal.pcbi.1005474. [Epub ahead of print]
Yang W1 Wen L2 Li SL2 Chen K3 Zhang WY2 Shaman J1.
Measles is a highly contagious and severe disease. Despite mass vaccination it remains a leading cause of death in children in developing regions killing 114900 globally in 2014. In 2006 China committed to eliminating measles by 2012; to this end the country enhanced its mandatory vaccination programs and achieved vaccination rates reported above 95% by 2008. However in spite of these efforts during the last 3 years (2013-2015) China documented 27695 52656 and 42874 confirmed measles cases. How measles manages to spread in China-the worlds largest population-in the mass vaccination era remains poorly understood. To address this conundrum and provide insights for future public health efforts we analyze the geospatial pattern of measles transmission across China during 2005-2014. We map measles incidence and incidence rates for each of the 344 cities in mainland China identify the key socioeconomic and demographic features associated with high disease burden and identify transmission clusters based on the synchrony of outbreak cycles. Using hierarchical cluster analysis we identify 21 epidemic clusters of which 12 were cross-regional. The cross-regional clusters included more underdeveloped cities with large numbers of emigrants than would be expected by chance (p = 0.011; bootstrap sampling) indicating that cities in these clusters were likely linked by internal worker migration in response to uneven economic development. In contrast cities in regional clusters were more likely to have high rates of minorities and high natural growth rates than would be expected by chance (p = 0.074; bootstrap sampling). Our findings suggest that multiple highly connected foci of measles transmission coexist in China and that migrant workers likely facilitate the transmission of measles across regions. This complex connection renders eradication of measles challenging in China despite its high overall vaccination coverage. Future immunization programs should therefore target these transmission foci simultaneously.
DOI: 10.1371/journal.pcbi.1005474