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California Shuts Out Fujian 54-0 in H3N2 Influenza A Battle

Recombinomics Commentary
February 19, 2005

The California strain of H3N2 has shut out Fujian for the second week in a row.  Each week the CDC lists the viruses isolated at its sentinel labs which track human influenza in the United States.  The H3N2 sub-type of influenza A usually causes the most severe disease, and it is the human sub-type that has been changing most rapidly worldwide.  The change has been very dramatic this year in the United States.

The H3N2 sub-type received considerable attention two years ago due to controversies over the selection of the vaccine sub-type.  Since 1999 the Panama version (A/Panama/2007/99) had been used as the H3N2 component in the trivalent human vaccine. 

In 2002 a new variant (A/Fujian/411/2002), isolated from Fujian province in China began to appear at surveillance labs worldwide.  At this time in 2003 it was clear that Fujian should replace Panama, but there were technical difficulties in growing the virus without first passaging it through a cell line.  However, since such a procedure had not been approved by regulatory agencies, the initial passage through the cell line created problems so Panama was used in the 2003 vaccine.  As expected Fujian displaced Panama in the 2003/2004 season in the US and 80% of the H3N2 isolates were Fujian.  That season saw an unusually high number of deaths in children.

This season Fujian-like H3N2 was used in the human vaccine (in the US a Fujian like strain from Wyoming, A/Wyoming/3/2003, was used).  However, Fujian began to be replaced in the southern hemisphere by a variant isolate in Wellington (A/Wellington/1/2004), and that strain was used to make the 2005 vaccine for the Southern Hemisphere.

In the US however, a new variant isolated in California (A/California/7/2004) has begun replacing Fujian.  The change has been dramatic.  By the end of the first week in 2005 there had been 88 H3N2 isolates in the US that had been sub-typed, and all were Fujian.  In the next week there were 24 Fujian and 6 California isolates.  By week 4 California had become more dominant with 26 new isolates compared to 9 Fujian.  For the past 2 weeks, it's been all California, with 17 more isolates last week, and 54 more this week.

Most of the recent isolates have been from the east coast, where recent childhood deaths associated with influenza A have been reported.

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