The deadly bird flu virus has returned in a mutant strain with unpredictable risks to human health, the UN Food and Agriculture Organisation (FAO) warned on Monday.
FAO urged for a heightened state of readiness and widespread surveillance against the return of the highly pathogenic H5N1 avian influenza virus, amid signs that a mutant strain has been spreading across Asia and beyond.
The H5N1 virus has infected 565 people since it first appeared in 2003, killing 331, with the latest death occurring earlier this month in Cambodia.
FAO Chief Veterinary Officer Juan Lubroth said a cause for concern was the appearance in China and Viet Nam of a variant virus apparently able to side-step the defences provided by existing vaccines.
In Viet Nam, which suspended its springtime poultry vaccination campaign this year, most of the northern and central parts of the country, where H5N1 is endemic, have been invaded by the new virus strain, known as H5N1 – 126.96.36.199.
Head of the Animal Health Department's Epidemiology Office Van Dang Ky confirmed that it was not a new virus strain but a mutation of the H5N1 virus which has been found in the northern part of Viet Nam late last year.
"Relevant agencies raised warning over the virus after discovering it and asked local authorities to take measures to prevent it from spreading," he said.
"Animal health forces have always kept close surveillance over the virus and have taken preventive measures for domestic poultry, focusing on vaccination," he said.
From the start of the year, 50 million doses of vaccine against H5N1 virus for poultry have been imported and up to 45 million doses of vaccine have been used.
"However, the problem is that no vaccine against the new virus strain has been developed and Vietnamese scientists are researching how effectively vaccinate against it," Ky added.
Viet Nam's veterinary services are on high alert and are reportedly considering a new, targeted vaccination campaign this fall.
The countries where H5N1 is still firmly entrenched – Bangladesh, China, Egypt, India, Indonesia and Viet Nam – are likely to face the biggest problems, but no country can consider itself safe.
"Preparedness and surveillance remain essential. No no one can let their guard down with H5N1," Lubroth said.