WHO recommended H5N1 prototype strains for influenza pandemic vaccine development remain the same

28 October 2005

The WHO Global Influenza Programme has been closely monitoring the antigenic and genetic evolution of circulating H5N1 viruses, especially human isolates. Recent investigations have indicated that H5 haemagglutinins (HA) genes of viruses from birds in China, Indonesia, Japan, Mongolia, Russia, South Korea and Turkey, and 3 viruses from humans in Indonesia are genetically distinguishable from the prototype strains selected last year for influenza pandemic vaccine development. There is also evidence of antigenic variation among the HA of recent viruses. However, their geographical spread and pathogenicity in human populations remain unclear.

At present WHO does not recommend changing the previously selected H5N1 prototype strains for ongoing pandemic vaccine development. But, for vaccine research purposes, the WHO H5 Reference Laboratory Network, which undertakes the tasks of selecting and developing the pandemic vaccine strains, has initiated the development of experimental H5N1 vaccine prototype strains from the recent viruses.

Analyses of more recent viruses, from both animals and humans, are urgently needed in order to obtain a better understanding of the evolution of the viruses and their antigenic relationships. WHO once again calls for rapid sharing of avian influenza virus isolates/specimens from affected Member States with the WHO H5 Reference Laboratory Network.

See also Previous review, July 2005