Vietnam's government has halted a nationwide poultry vaccination against H5N1, saying a new strain of the virus has rendered the current vaccine ineffective.

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"Based on post-vaccination surveillance results, a new clade of the H5N1 virus has appeared in Vietnam since 2010," said the government. The new strain has been found in northern provinces, coastal provinces in the central region and the Central Highlands. The old strain is still active in the southern provinces of Vietnam, according to reports.