Human Infection with Avian Influenza

Since the beginning of 2004, 16 confirmed cases of H5N1 infection have been reported in Thailand, of which 11 have been fatal.

Four of these cases have occurred during the past four week, suggesting that human infection is now occurring at a faster rate. Investigations have identified exposure to diseased chickens as the most likely cause of infection. Recently, Thai officials announced a probable case of human-to-human transmission in a family cluster of cases. Analysis of specimens from this cluster is now under way at a laboratory collaborating with the World Health Organization (WHO, Geneva, Switzerland) to determine whether the virus has changed its genetic makeup. So far, there is no evidence that sustained human-to-human transmission is occurring in Thailand.

According to WHO, countries experiencing outbreaks need to rapidly share human and animal viruses with laboratories in the WHO Global Influenza Surveillance Network. Analysis of these viruses determines the possible need for changes in the prototype vaccine "seed” strains that WHO makes available to the pharmaceutical industry. Companies also need to engage in research on pandemic vaccine development, including pilot production of small batches for clinical testing. WHO notes that companies may be reluctant to produce a vaccine for a pandemic that cannot be predicted with any certainty and might not be caused by circulating strains.

WHO made the prototype seed strain for an H5N1 vaccine available to manufacturers at the beginning of April 2004, but to date only two of the 12 major companies producing influenza vaccines have taken work on a pandemic vaccine forward. While these two companies (Chiron and Aventis Pasteur) have produced small batches of vaccine for use in clinical trials, the trials are not expected to begin before the end of the year.




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