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Saturday, November 29, 2003Moreover, the long time now required to develop and mass produce a vaccine in enough quantity to protect large populations would be a serious vulnerability in any strategy for responding to such an outbreak. The customary way to make a vaccine against a specific influenza virus is to let viral genes mix inside chicken eggs that include genes from a virus known to be safe to use in humans. Viruses arising from this mixing that are both safe to use in humans and carry hemagglutinin (H) and neuraminidase (N) proteins that trigger immune system responses in humans are used to make vaccines. "In the event of a pandemic, the process of initially developing a "seed" virus suitable for mass production as a vaccine would be too slow and too dependent on a steady supply of eggs," said Richard Webby, Ph.D., assistant member of the St. Jude Division of Virology and co-author of the Science article. Particularly worrisome is the fact that the highly pathogenic H5 and H7 subtypes of the flu virus kill embryonated chickens eggs. However, Webster's laboratory demonstrated earlier this year that it is possible to dramatically reduce the overall vaccine development time by using a new technique to develop the seed virus. Led by Webby, the St. Jude team successfully modified a technique called reverse genetics to develop a seed vaccine against H5Nl. The researchers mixed two genes from H5Nl with six genes from a second virus (A/PR8/34)[HINI]) to produce a seed vaccine virus that was safe in humans but that carried the H and N proteins that stimulated the immune system. "Although the viruses still have to be grown up in eggs to make vaccines, the initial process of making the seed vaccine is much quicker using reverse genetics," Webby said. But reverse genetics requires specific populations of animal cells in which to grow the viruses, and there are only a few lines of cells suitable for this process. Most of those cell lines are owned by large pharmaceutical companies rather than academic research laboratories such as St. Jude. On the other hand, Canada's ready: Federal and provincial health officials are finalizing a new pandemic influenza plan that could call for the stockpiling of huge amounts of anti-viral drugs and the establishment of old-fashioned 'fever hospitals,' last seen during the Spanish Flu of 1918. The plan would stop short of ordering mass flu vaccinations, sources say. 'If a killer strain hits us, there won't be time to get a workable vaccine ready,' said a senior Ontario health official. 'SARS gave us a taste of what to expect.'" And just how serious is the influenza disease outbreak so far? Here's the latest data from the CDC (for the week of November 15): The proportion of patient visits to sentinel providers for influenza-like illness...overall was 3.3%, which is above the national baseline of 2.5%. The proportion of deaths attributed to pneumonia and influenza was 6.1%, which is below the epidemic threshold for the week. In contrast, this is where things stood last year at the same time: The proportion of patient visits to sentinel providers for influenza-like illness...overall was 1.1%, which is less than the national baseline of 1.9%. The proportion of deaths attributed to pneumonia and influenza was 6.8%. And two years ago: The overall proportion of patient visits to sentinel physicians for influenza-like illness... was 1.2%, which is less than the national baseline of 1.9%. The proportion of deaths attributed to pneumonia and influenza was 6.6% So, it looks like it's just a little more prevalent than usual, and about as deadly as usual. Hardly cause for alarm. posted by Sydney on 11/29/2003 07:02:00 PM 0 comments 0 Comments: |
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