The genetic sequencing analysis of viruses taken from two Vietnamese sisters showed that there are no possibilities of person-to-person transmission of bird flu, according to the World Health Organization (WHO).

"WHO has today received the results from a study of virus isolated from a 23-year-old woman who is part of a family cluster in Vietnam under investigation as the first possible instance of human-to-human transmission. Virus genetic material from this woman, as for the other case in this cluster, is of avian origin and contains no human influenza genes," it announced on its website on Thursday (Feb 12th).

Earlier, the organization announced a similar testing result for other case in the cluster, 30-year-old sister of the 23-year-old woman.

The findings indicate that H5N1 has not changed to a form easily transmitted from one person to another, it said, adding that "no illness has been reported in other family members, in the local community, or in health workers involved in care of these patients."

However, Bob Dietz, spokesman of WHO in Vietnam, told Xinhua on Thursday that, "The results are encouraging, but unfortunately, they are still not the conclusive proof we need to fully discount the possibility of human-to-human transmission of the H5N1 virus."

Pascale Brudon, representative of WHO in the country, echoed his statement by saying that the results did not exclude a very limited person-to-person transmission of H5N1.

The cluster involves a 31-year-old man, his two sisters, and his 28-year-old wife in Vietnam's northern Thai Binh Province. Theman named Ngo Le Hung, a schoolteacher, died on Jan. 12 in the Hospital of Tropical Diseases in the capital city of Hanoi.

After having a temperature on Jan. 6, Hung was admitted to the Thai Binh Hospital which said he had showed symptoms of flu for three days. On Jan. 9, provincial doctors decided to transfer him to Hanoi. In the city, he was cared by many people, including two of his younger sisters, Ngo Le Hanh and Ngo Le Hong, his newly-wed wife named Phung Thi Ngoc Anh, and his mother-in-law Nguyen Thi Nguyet.

One day after Hung's death, his sisters and Ngoc Anh were hospitalized, although his wife had no symptoms of flu. Then, the wife was discharged from hospital, but both of the two sisters died on Jan. 23. The two sisters were confirmed to have contracted H5N1. Meanwhile, no samples of his brother were available for testing since his body was cremated.

Editor: Wing