The bird flu virus strain H5N1 in Vietnam has experienced slight genetic changes with milder virulence, local newspaper People's Army reported on Wednesday.

Compared with H5N1 in Vietnam in early 2004, the percentage of the virus' genes which determine its virulence has decreased to 98.2 percent from 99.1 percent, according to the findings of a recent research by the country's National Institute for Hygiene and Epidemiology .

The slight genetic changes could have helped H5N1 adapt itself better to humans, which has led to more cases of infections but with less severe symptoms and lower fatality rates, said Nguyen Thuy Hoa, head of the institute's Epidemiology Department.

The disease has attacked local people at different ages with the youngest infection case being four months old and the oldest 81 years old, but most of the victims are aged under 40, especially in the age bracket of 10-19. The fatality rate in the northern region is 38.1 percent, and that in the southern region 83.3 percent.

Vietnam's Health Ministry on Tuesday announced that the country has detected 65 human cases of H5N1 infections, including 22 fatalities, in 25 cities and provinces since December 2004, bringing the total respective numbers since December 2003 to 92 and 42.

The ministry also said a 15-year-old boy named Vu Van Hoa from northern Hai Phong city has been infected with the virus strain H5.Further tests are being done to define whether he was infected with H5N1 or not.

Now, the patient from Tien Lang district, whose bird flu symptoms started to appear on Nov. 14, no longer has fever and breathing difficulty, the ministry said, noting that he is under treatment at the Central Pediatrics Hospital in Hanoi capital.