The WHO H5 Reference Laboratory Network and WHO Collaborating Centres and Reference Laboratories have reviewed available data to assess the suitability of the H5N1 prototype strains selected by WHO last year for influenza A/H5N1 pandemic vaccine development. The results of genetic and antigenic analyses of 2004 and 2005 human and animal A/H5N1 viruses received from affected countries, did not provide any convincing evidence to change the WHO recommended A/H5N1 influenza vaccine prototype strains. Therefore, the WHO recommendations from April 2004 are still valid.

WHO will continue to monitor the antigenic and genetic changes in circulating A/H5N1 viruses, especially in humans. For research purposes, the WHO Collaborating Centres will develop experimental prototype vaccine strains from recent human influenza A/H5N1 viruses.

The timely selection and verification of suitable H5N1 prototype vaccine strains depends primarily on close collaboration between the affected countries and WHO, especially as regards the rapid sharing of A/H5N1 virus/specimens, particularly from humans, and exchange of analytical data.