MRC National Institute for Medical Research, London
Science for Health
Scientists discover the travel patterns of seasonal flu
18 April 2008
The research was led by Cambridge University and the World Health Organisation (WHO) Global Influenza Surveillance Network, which is an international team of researchers from Europe, Australia, Japan and the United States and includes the World Influenza Centre at NIMR. They analyzed 13,000 samples of influenza A (H3N2) virus, collected across six continents from 2002 to 2007 by the WHO's Surveillance Network. This subtype of influenza is currently the major cause of flu-related illness and death in humans. The researchers compared physical differences in a surface protein, called hemagglutinin, across the different samples. Hemagglutinin is the primary target of the immune response, and even small changes can allow the virus to evade the immune system and cause disease.
One of the challenges to creating flu vaccines is that the global migration pattern of influenza viruses has been incompletely understood. Several competing hypotheses have emerged including migration between the Northern and Southern hemispheres following the seasons, migration out of the tropics where influenza viruses were thought to circulate continuously, and migration out of China.
The Science study shows instead that each year since 2002, influenza A (H3N2) viruses have migrated out of what the authors call the “East and Southeast Asian circulation network,” and from there spread around the world. These findings suggest that by focusing surveillance efforts on East and Southeast Asia, researchers may be able to extend their forecast of the flu strains most likely to cause epidemics, which may in turn help experts decide which strains should go in the flu vaccine each year.
This extensive analysis of the worldwide circulation of influenza viruses over a five-year period by the WHO Global Influenza Surveillance Network reinforces the previous notion that many new variants of influenza viruses emerge in east and south-east Asia, and the importance of intensive surveillance of viruses in that region for biannual decisions of the most appropriate composition of influenza vaccines.
Dr Alan Hay, Director of NIMR's World Influenza Centre
Flu epidemics appear to be driven by seasonal factors such as winter, or rainy seasons. So there can be cities that are only 700 miles away from each other, such as Bangkok and Kuala Lumpur, which have epidemics six months apart. There is a lot of variability like this in East and Southeast Asia, so lots of opportunity for an epidemic in one country to seed an epidemic to another nearby country, like a baton passed by runners in a relay race. The ultimate goal of our collaboration is to increase our ability to predict the evolution of influenza viruses. This study is one step along that path and in particular highlights the importance of ongoing collaborations and surveillance in East and Southeast Asia, and of expanding these collaborations in the future.
Derek Smith of the University of Cambridge, corresponding author of the study
The flu virus is constantly mutating, so it’s a major challenge for public health as well as a fascinating example of evolution in action. This study advances our knowledge of how new flu strains spread across the globe and how epidemics arise.
Katrina Kelner, Science’s deputy managing editor, life sciences
Original article
The research findings are published in full in:
Colin A. Russell, Terry C. Jones, Ian G. Barr, Nancy J. Cox, Rebecca J. Garten, Vicky Gregory, Ian D. Gust, Alan W. Hampson, Alan J. Hay, Aeron C. Hurt, Jan C. de Jong, Anne Kelso, Alexander I. Klimov, Tsutomu Kageyama, Naomi Komadina, Alan S. Lapedes, Yi P. Lin, Ana Mosterin, Masatsugu Obuchi, Takato Odagiri, Albert D. M. E. Osterhaus, Guus F. Rimmelzwaan, Michael W. Shaw, Eugene Skepner, Klaus Stohr, Masato Tashiro, Ron A. M. Fouchier, and Derek J. Smith. (2008)
The Global Circulation of Seasonal Influenza A (H3N2) Viruses
Science, 320, 340-346 Abstract
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