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Maryn McKenna writing for CIDRAP News has the details of two studies released yesterday that show the similarities between the novel H1N1 virus of 2009 and the pandemic virus of 1918.
While sharing the same classification (H1N1) as one of the two seasonal influenza `A’ strains that have been in circulation for decades, novel H1N1 was genetically different enough that those under the age of about 50 had little or no immunity.
Now, scientists are beginning to fathom why that is so.
This from CIDRAP News.
Study shows 1918 and 2009 pandemic viruses share key feature
Maryn McKenna
Contributing Writer
Mar 24, 2010 (CIDRAP News) – Structural similarities between the pandemic flu viruses of 1918 and 2009 may explain older adults' apparent immunity to the newer virus, two scientific teams report today in two journals. Their results may also explain how pandemic viruses evolve into seasonal viruses, and could point the way toward development of future pandemic vaccines.
Writing in Science Express, the online ahead-of-print arm of the journal Science, Ian Wilson and Rui Xu of the Scripps Research Institute and colleagues from Vanderbilt University and Mount Sinai School of Medicine say that the 1918 and 2009 pandemic viruses are antigenically close, with hemagglutinin proteins that share similar crystalline structures. In contrast, the hemagglutinins in 24 seasonal flu strains dating from the 1930s through the 1950s, and 9 seasonal-vaccine strains from 1977 through 2007, differed from the pandemic strains by 30% to 58% of their amino-acid sequences.
The similarity between the two pandemic viruses is unusual, not only because they are separated by so many years, but also because genetic evidence has shown that the 2009 pandemic virus was not brand-new, but had already been circulating in humans—two circumstances that would have been expected to cause the viruses to diversify as they adapted.
Helen Branswell, writing for the Canadian Press, also has terrific coverage of this story. Both reports are well worth reading in their entirety.
H1N1 virus more like 1918 flu than modern cousins; explains infection patterns
Provided by: Canadian Press
Written by: Helen Branswell, Medical Reporter, THE CANADIAN PRESS
Mar. 24, 2010
TORONTO - The pandemic H1N1 virus more closely resembles the 1918 Spanish flu virus than more modern cousins in the same flu family, new research shows - a finding which helps explain the age pattern of H1N1 infections.
Like the Spanish flu virus, the pandemic H1N1 lacks two sugar coats seen on contemporary viruses from the same family, the work reveals.
The two studies, released Wednesday, confirm that antibodies which protect against the pandemic virus also fight the virus that caused the 1918 pandemic. But they are not able to neutralize seasonal H1N1 viruses, nor are 2009 H1N1 viruses stopped by antibodies generated in response to those recent viruses.
