25 November 2013
Flu outbreaks could be better controlled with vaccination campaigns timed to match differing regional disease patterns, according to findings from the Fogarty International Center at the U.S. National Institutes of Health. Fogarty scientists collaborated with the Chinese Centers for Disease Control in the work.
“This research suggests the need for staggered timing of vaccination in three broad epidemiological regions,” said Dr. Cecile Viboud, who co-authored the study with Fogarty colleagues and Chinese collaborators.
In northern China, flu season coincides with winter outbreaks in the world’s other northern temperate zones, where vaccinations are recommended to begin in October. Flu typically begins circulating in the colder months that follow, as people spend more time in enclosed spaces, where viruses more readily pass from person to person.
Southern China is different. Flu outbreaks in the warmer regions typically occur in the spring, and the study finds that a vaccination campaign beginning in February is likely to yield the best results. Outbreak patterns in an intermediate zone between these two regions are more complex and will require further research to better understand.
China introduced seasonal influenza vaccination in 1998. The campaign is not yet countrywide, and just about 2 percent of the population is routinely immunized. Health workers in Beijing and a few other cities now vaccinate the most vulnerable populations — older adults and school-age children. It is estimated that influenza annually causes 11–18 deaths per 100,000 people in China, with underdeveloped rural areas suffering two to three times higher flu-related death rates.
More research will be needed to confirm the optimal vaccination policy, particularly for the mid-latitude provinces around Shanghai, the authors said.
“Before a national influenza vaccination program can be established in this large, climatologically diverse country, public health experts need a clear picture of influenza seasonally across the country that could be used to optimize the timing of a future Chinese vaccination effort,” Viboud said.
Previous studies have shown that while cold temperatures and low humidity favor influenza transmission in temperate settings, flu seasons in tropical climates coincide with periods of high rainfall. Intermediate regions sometimes have twice-annual epidemic cycles, rather than the single season observed in the United States and Europe, for example.
Hospitals in cities in each of China’s 30 provinces provided data from 2005 to 2011 that formed the basis for these conclusions. Researchers used statistical analyses to distinguish the three epidemiologically distinct flu regions.
The need for identifying regional differences in flu outbreaks is important as more low- and middle-income countries aim to launch national influenza immunization programs, the Fogarty announcement said.
The findings on China’s flu patterns are part of a larger international study underway since 2001, the Multinational Influenza Seasonal Mortality Study (MISMS). Flu causes some 250,000–300,000 deaths each year, according to the World Health Organization, and about 3 million to 5 million cases of severe illness. That level of sickness also puts considerable pressure on public heath resources and affects workplace productivity and economic activity.
MISMS is working to better understand the seasonal variations associated with influenza patterns both within and amongst countries. International researchers conducting this work also learn more about the circulating subtypes of flu virus and how they move about the globe. The ultimate MISMS goal is to develop a world map of influenza mortality burden and seasonal patterns.