Characterization of Regional Influenza Seasonality Patterns in China and Implications for Vaccination Strategies: Spatio-Temporal Modeling of Surveillance Data

Abstract

Cécile Viboud and colleagues describe epidemiological patterns of influenza incidence across China to support the design of a national vaccination program. Please see later in the article for the Editors' Summary

Mortality burden from seasonal influenza and 2009 H1N1 pandemic influenza in Beijing, China, 2007‐2013

“…We defined an influenza season as the period ranging from the 27th week in 1 year to the 26th week in the next year, based on influenza surveillance data 11. The registration system categorized weekly numbers of deaths into two underlying causes of death according to the International Classification of Disease, Tenth Revision [ICD‐10]: respiratory (ICD‐10 codes J00‐99) and circulatory diseases (ICD‐10 codes I00‐99) (respiratory and circulatory: R&C), and all‐cause deaths (including both respiratory and circulatory deaths which have been previously been associated with influenza‐associated deaths) 2, 3, 4, 5, 6. Two age groups were considered: <65 years and ≥65 years.…”

“…Although several statistical models have estimated the mortality burden of influenza,2 few have focused on mainland China,3, 4, 5 and information on mortality burden in northern China is especially limited. Considering the diverse seasonality patterns,6 income levels and healthcare access across China, mortality burden may vary by region.…”

Influenza‐associated mortality in Yancheng, China, 2011‐15

“…Yancheng is situated in Jiangsu province, just north of the Yangtze river delta in eastern China where more than 100 million people are clustered in the area surrounding Shanghai (Figure 1). Jiangsu province has a subtropical‐like pattern in influenza virus activity with a less obvious seasonal pattern, compared to the temperate northern part of the country where there are influenza epidemics each winter, and the southern provinces where there are summer epidemics 7. Limited attention has so far been given to the potential burden of influenza in Yancheng, as with most other cities in China, and influenza vaccine coverage is very low.…”

Timing and periodicity of influenza epidemics

“…Another prism by which the subtleties of influenza's weakly forced pendulum may be seen is from subtropical locales, some of which experience semiannual resurgences of influenza in winter and spring/summer, as is the case in Hong-Kong or Shanghai (18). It will be interesting to learn whether these could be related to nonlinearities in the absolute humidity response, or whether these represent geographic cross-roads in areas of low seasonal forcing combined with robust coupling to regions subject to pure annual influenza cycles, aligned with winters in the northern (Northern China, Europe and North America) and southern hemispheres (Southern China, Australia).…”

“…Future analyses may shed light on the complexity of the interplay among environmental factors, population coupling, and the occasional term-time forcing, in fine-tuning seasonality of epidemic and pandemic influenza globally. For this, it may be necessary to disaggregate influenza records by subtypes, as transmission patterns-and thereby seasonal forcing-are subtype-dependent (18,20). For example, multiannual cycles may occur in subtype-specific time series as immunity builds up to a particular influenza strain, even if aggregate dynamics are annual (Fig.…”