GENEVA (AFP) - The World Health Organisation (WHO) said Friday there was no need for a massive vaccine campaign against the bird flu virus (H5N1) because it has not been proven that it would become a pandemic.

"There is no evidence available that would say that we should begin vaccinating populations across the board with H5N1 at this point in order to prevent a pandemic because it is not known what may cause a pandemic," WHO Assistant Director General David Heymann told reporters.

H5N1, which has caused 209 deaths out 340 afflicted since 2003, is not the only virus that could start a flu pandemic, he added. Other viruses, such as H5, H7 or H9, pose the same threat, he said.

Heymann said many countries are considering a widespread vaccination campaign as part of a ´first protection´ barrier, which would act as an insurance plan for the population.

However, he recalled that the swine flu vaccinations in 1976 in the United States had a lot of side effects.

"So a country would have to weight whether or not that insurance policy of getting a lower level of immunity against a virus which could cause a pandemic is as important as the side effect which might occur from that vaccine," he said.

Earlier this month WHO responded to the case of a father and son in China dying from H5N1 earlier this month. There were three possible explanations for the father-son case: either they were infected by the same animal, by transmission between them, or by exposure to two different infected animals.

The deadly H5N1 strain has passed from human to human only in very rare cases but scientists fear that such transmission could become more efficient and widespread through mutation, causing a global pandemic.