The World Health Organisation (WHO) has warned that a possible outbreak of the bird flu pandemic could spread throughout the world and could kill between 2-7 million people.

The warning came following the recurrence of bird flu and worries that humans can be infected with avian influenza virus H5N1.

Vietnamese epidemiologists also expressed concern over the complexity of the virus. Dr Nguyen Tran Hien, acting director of the Central Epidemiology Institute, said according to scientists, an avian influenza epidemic takes place every 30-40 years.

In history, such epidemics broke out in 1918-1919, 1957-1958, 1968-1969 and this year. In addition, a new avian influenza strain, H5N1 Type A, was reported this year. This virus originated from birds. In 1997, the virus attacked poultry and then humans.

Dr Hien said scientists were worried about the emergence of a highly infectious strain of influenza for its complexity. Experts warned that H5N1 can transmit from chickens to humans, although direct transmissions are reportedly difficult. After that, the virus can combine with the existing strains of influenza in humans to change genetic factors and develop a new strain that can transmit from human to human. At that time, a terrible pandemic will be inevitable because people have no immunity. An influenza virus, originated from Spain, killed 40-50 million people throughout the world in 1918-1919.

According to scientists, bird flu virus spreads very quickly and it cannot be contained easily like SARS by quarantine methods. Virus H5N1 can exist in ice for a long time.

Bird flu virus can cause some symptoms in humans including high temperatures, cough, sore throat and muscle pain. Some patients get pains in eyes and acute pneumonia and bronchitis diseases. Currently, new medicines have been produced to stop the development of the virus in humans, including Tamiflu and Relenza.