Flu Then Flu Now: New Estimates on Pandemic Influenza Deaths
Flu Then Flu Now: New Estimates on Pandemic Influenza Deaths
Abstract & Commentary
By Joseph F. John, Jr., MD, FACP, FIDSA, FSHEA, Associate Chief of Staff for Education, Ralph H. Johnson Veterans Administration Medical Center; Professor of Medicine, Medical University of South Carolina, Charleston, SC, is Associate Editor for Infectious Disease Alert.
Dr. John does research for Merck, is a consultant for Cubist, Roche, and bioMerieux, and is on the speaker's bureau for Pharmacia, GSK, Merck, Bayer, and Wyeth.
Sources: Murray CJ, et al. Estimation of potential global pandemic influenza mortality on the basis of vital registry data from the 1918-20 pandemic: a quantitative analysis. Lancet. 2006;368:2211-2218.
Webster RG, Govorkova EA. H5N1-influenza — continuing evolution and spread. N Engl J Med. 2006;355:2174-2177.
Bresson JL, et al. Safety and immunogenicity of an inactivated split-virion influenza A/Vietnam/1194/2004 (H5N1) vaccine: phase I randomized trial. Lancet. 2006;267:1657-1664.
It has become in vogue to plan for influenza pandemics. What is not clear is what would be excess mortality in such a pandemic. Several studies have estimated mortality based on guesses of excessive influenza-related mortality. A new study from Harvard Initiative for Global Health made estimates of all excess mortality, assuming a pandemic with a highly virulent strain of influenza for countries with mortality like that of 1918-1920, for countries which had mortality data before and after the pandemic of 1918-1920.
The study was able to gather data from 28 countries that had recorded excess mortality during the years 1915-1923. The lowest excess mortality was in Colorado (1.0%) and the highest was in 2 states in India, Central Berar (7.8%) and United Provinces (7.1%). Wisconsin had an excess rate of only 0.25% so the increased mortality in Central India was 31 times that of Wisconsin.
Mortality was highest in young adults 15-35 years of age. Some countries had no excess mortality in persons > 60 years of age. Based on populations in 2004, India would have a median of over 12 million deaths, China about 9 million, Ethiopia 2.7 million, Nigeria 2.3 million, Brazil about 700,000, and the United States about 300,000. The median number of deaths worldwide would be about 62 million, based on the regression model used. When calculations were made for a pandemic occurring in one year, the increase in global mortality would increase by 114% with the highest mortality in the 15-29 year olds.
Commentary
It is true that this study used a type of worst scenario: a pandemic with a virus as virulent that caused the 1918-20 pandemic. Since nearly all individuals living were thought to be exposed by 1920, the authors also argue that modern travel and rapid human mixing would likely not alter the estimates. They also concede that with modern medical care, particularly with intensive care, mortality would likely be lower. Use of antivirals may block some transmission and save additional lives. Vaccination with as long a preparation period of 4-6 months still could alter the epidemic. Finally, deaths in 1918-1920 were commonly due to bacterial pneumonia, so much so that Haemophilus influenzae took its name from its common appearance in the post-mortem lungs of pandemic influenza victims.
What should clinicians as well as public health officials do with these data? First, these high rates of death in no way relate to the probability of such a pandemic occurring. It is somewhat reassuring from my purview that the only "dramatic change in human health" occurred with the 1918-1920 pandemic. Nevertheless, lesser pandemics are probably realizing the penchant for change in the influenza virus. Currently an avian H5N1 virus is making a worldwide reach. It is also possible that while the world watches the global spread of H5N1 from Central China to Japan and Europe, waiting in the wings may be other novel influenza viruses that are much more capable of causing human to human transmission. To avoid catastrophic consequences, these studies suggest a focus on less developed countries where mortality would be highest. Recent H5N1 vaccine trials showed, however, efficacy and short term safety. So there is every reason to hope that modern vaccine development and implementation will buffer the effect of rapid pandemic spread that was so lethal early in the 20th century.
It has become in vogue to plan for influenza pandemics. What is not clear is what would be excess mortality in such a pandemic.Subscribe Now for Access
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