New virus evades current poultry immunization measures

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bird flu vaccineA new strain of vaccine-resistant H5N1 bird flu virus has emerged in China and is spreading through southeast Asia, Hong Kong researchers report.

"The implications are that current control measures are ineffective with dealing with the evolutionary changes that H5N1 undergoes," warned Dr. Yi Guan, director of the State Key Laboratory of Emerging Diseases at the University of Hong Kong and lead author of a report in this week's issue of the Proceedings of the National Academy of Sciences.

The new strain has become dominant throughout the region, replacing other variants of the virus, the report said.

"We think that this virus is likely to have already instigated a third wave of H5N1 infection in this region, as it is already widespread in southern China and has also been detected in other neighboring countries," Guan said.

The reason for the new strain's dominance is that "it was not as easily affected as other strains by the avian vaccine used to prevent H5 infection," the Hong Kong expert said. "What this means is that H5 avian vaccines are not able to prevent infection by this virus as efficiently as they do with other strains of H5N1."

"This is the kind of information you can get from cooperative surveillance," noted Karen Lacourciere, a program officer in influenza at the U.S. National Institute of Allergy and Infectious Diseases. "You can identify possible infection sources and points of intervention for a possible pandemic."

The new strain was also responsible for recent human infections by the avian flu virus in both rural and urban areas of China, the Hong Kong team reported. Human infections in urban areas could lead to a serious outbreak, challenging current plans aimed at preventing a human pandemic, they said.

The immediate danger is to stocks of chickens and other poultry, Guan said. "This study suggests that reliance on a single vaccine against H5N1 over a number of years, which is currently practiced, is unlikely to adequately control this disease in poultry," he said. "Therefore, the methods of poultry vaccination must be addressed."

China has a compulsory program of chicken vaccination, but the new strain evades that program, the researchers said. The fear is that it could spread to infect poultry throughout Asia and Europe, and perhaps jump to infect humans.

"The most important thing that can be done now is to increase systematic influenza surveillance in poultry over those affected regions," Guan said. "By doing this, we will be able to determine the dynamics of the spread of this virus."

In addition, the strains of bird flu virus used in poultry vaccines should be assessed regularly and changed if necessary, he said. "It is also possible that poultry vaccines may need to be tailored to effectively neutralize the particular strain of virus that is present in a particular region," Guan said.

Like Guan, Lacourciere said the finding "emphasizes the need for early surveillance. Early detection is important for understanding of the transition and spread of the virus."

"We continue to look at vaccine strategies," she added. "We want a vaccine that is broadly protective against different strains. Looking at preserved proteins might make possible a vaccine that offers universal protection."