What Is Yamagata Flu?

History

• The most common varieties of B strain flu virus worldwide have been the Yamagata and Victoria strains in recent years. After the Yamagata virus was first identified in Japan in 1988, this strain of flu began spreading around the world between 1990 and 2001. Most cases of influenza during those 11 years was linked to Yamagata flu. However, another B virus strain called Victoria, was also circulating, but mostly just in Asia, not worldwide like Yamagata.
  
  Since 2001, both B viruses been found to be the cause of the flu worldwide. Some years Victoria B is more prominent, and other years it is Yamagata B. Each year, flu vaccines are formulated to match the evolving prominent strains of the viruses that circulate around the world.
  
  Every February, officials of the World Health Organization (WHO) and U.S. Food and Drug Administration (FDA) meet to study and recommend which A and B strains should be put into the fall vaccine, giving drug companies time to process enough doses.
  
  

Significance

• In years past, the strains chosen for the following season's vaccine have been fairly accurate. However, more recently, the newly created vaccines do not have the right strain of A or B virus that is prominent during flu season. This causes the vaccine to be ineffective for fighting the flu. Records of the Centers for Disease Control and Prevention (CDC) show the incorrect B strain was picked for the vaccine in five of the last seven seasons, from 2001-02 through 2008-09.
  
  

Considerations

• During the 2007-08 flu season in the United States, the FDA and WHO picked a Victoria B strain to be put into the vaccine, based on the activity and history of the flu in the Southern hemisphere that year. But by the end of the 2007-08 flu season, most of the people infected with the flu were found to have Yamagata B strain. The vaccine was ineffective.
  The 2008-09 flu vaccine was mismatched again. Because of the 2007-08 mismatch, it was recommended to use more Yamagata B in the 2009 vaccine. However, the Victoria B strain became the predominant flu again during that flu season, and the vaccine was once again mismatched and ineffective.
  
  

Flip a Coin

• Even the FDA acknowledges that trying to determine whether to use Yamagata B strain or Victoria B strain in each new vaccine is working out to be nothing more than a guess. Dr. Melinda Wharton of the FDA's Vaccines and Biological Products Advisory Committee referred to the choice as "the annual agony of trying to flip the coin" to pick a B strain for the vaccine, according to a transcript of the committee's Feb. 21, 2008, meeting.
  
  

Prevention/Solution

• In light of the most recent flu concerns of H1N1, an A strain, flu vaccines and their formulations are becoming even more scrutinized. Whether or not Yamagata will end up in upcoming vaccines will still depend upon the previous year's dominance of the type B strain, but the determination process may change in the near future.