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1957 H2N2 Pandemic Flu Recalled from Proficiency Kits
April 13, 2005
>> It was not immediately clear why the 1957 pandemic strain, which killed between 1 million and 4 million people - was in the proficiency test kits routinely sent to labs.
It was a decision that Stohr described as "unwise," and "unfortunate."
That particular bug was "an epidemic virus for many years," Stohr said from the U.N. health agency's headquarters in Geneva, Switzerland. "The risk is low but things can go wrong as long as these samples are out there and there are some still out there."
The 1957 strain has not been included in the flu vaccine since 1968, and anyone born after that date has no immunity to it.<<
Clearly, sending H2N2 to labs around the world for proficiency testing is not a good idea. The virus caused a pandemic in 1957 and exposure by a younger population could have significant consequences. Those most impacted would be born after 1968, and a high percentage of laboratory technicians would fall into the age susceptible group.
Details on the discovery of the virus in samples not linked to the test kit would be useful in determining how widespread the virus is in samples not being destroyed.
Transmission of the virus would likely be somewhat limited. The H2 serotype has been virtually absent from human populations since 1968. This elimination was likely due to immunity to earlier outbreaks as well as vaccinations with H2N2. The current trivalent vaccine includes H1 (H1N1) and H3 (H3N2) serotypes of influenza A. H2 is no longer included because it is not circulating in human populations.
The recall of 1957 H2N2 raises issues related to WSN/33 in Korean swine. Although H1N1 is still circulating in the current trivalent vaccine, WSN/33 was isolated in 1933 and is markedly different than the contemporary H1N1 in circulation. Moreover, it has key mutations that would increase its virulence and broaden its tropism. WSN/33 was isolated from mouse brain in 1940 and is missing a key glycosylation site on NA. This mutation allows the virus to sequester plasminogen, which facilitates HA cleavage and allows the virus to enter a broad range of tissue types. It is also lethal in mice, and contains a mutation in M2 that makes it resistant to antiviral ion channel blockers such as Amantadine and Rimantadine.
Sequences from swine on farms in South Korea were deposited at GenBank October 24, 2004 and the WHO has been investigating the sequences for the past six months. They are expected to issue a report announcing the halt of efforts to prove or disprove the existence of the reported viruses with WSN/33 genes in Korean swine.
Remarkably, after 6 months there still has not been positive data generated to prove or disprove the existence of the reported virus.
If these viruses are in swine in South Korea, they would raise serious public health concerns. How they moved from a lab to Korean farms would also be a major concern, since either an accident or bioterrorism could have significant consequences.
WHO's failure to generate positive data to confirm or refute the existence of WSN/33 genes in pigs on farms in Korea is cause for concern.