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 | | Influenza virons, magnified approximately 100,000 times. Outbreaks of influenza A are seeded by viruses originating in Asia according to new research |
The assumption is that pandemic influenza is an exceptionally deadly form of seasonal flu, however Peter Doshi from MIT says this is hard to support. He has conducted a study that challenges common beliefs about the flu - in particular that the US Centers for Disease Control and Prevention claim that “the hallmark of pandemic influenza is excess mortality.”
He based his study on an analysis of more than a century of influenza mortality data and found that the peak monthly death rates in pandemic seasons were no higher than - and were sometimes exceeded by - those for severe nonpandemic seasons.
Doshi suggests one of the reasons that pandemic flu might be so misunderstood is that commercial interests may be playing a role in inflating the perceived impact of pandemics.
“With public policies such as universal vaccination being discussed and more than $5 billion of federal money spent on preparing for the next pandemic, the study raises many important questions of public policy,” he said.
Despite Doshi’s theory - the fact remains that flu is a deadly disease that affects people worldwide. According to the World Health Organisation, Annual influenza epidemics are thought to infect 5 - 15% of the world population each year and, despite vaccination programmes, cause 3 - 5 million cases of severe illness and between 250,000 - 500,000 deaths.
One of the serious challenges to creating flu vaccines is that the global migration pattern of influenza viruses has been a mystery. 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.Now, Scientists at the University of Cambridge have found that each year since 2002 influenza A (H3N2) viruses have migrated out of what they call the “East and Southeast Asian circulation network” and spread throughout the world. The team found that new strains emerge in East and Southeast Asia and then about six to nine months later reach Europe and North America. Several months later still, the strains arrive in South America.
Lead author of the study, Derek Smith of the University of Cambridge, emphasised that the flu vaccine works very well, and protects the 300 million people vaccinated each year. But, from time to time, a new strain emerges after the vaccine strain selection has already been made.
“The ultimate goal of our work 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 expanding these collaborations in the future,” said Smith.
Whether a flu outbreak is classed as a pandemic or not is unimportant in the battle to vaccinate the population said Elias A. Zerhouni, MD, director of the U.S. National Institutes of Health. “By applying an innovative strategy to map differences in seasonal influenza strains worldwide, Smith and his colleagues have offered important insights into patterns of influenza virus spread that could greatly improve surveillance and vaccine strain selection,” he said. |
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