Few patients in Japan, who had type B influenza, normally a milder flu causing smaller outbreaks than the more common type A, showed signs of resistance to the drugs Tamiflu and Relenza. It also worries doctors who now say they would need to find new medicines to treat drug-resistant flu if the viruses start spreading.
Many experts also believe that Japanese doctors prescribe anti-flu drugs frequently, which gives viruses a chance to evolve. Doctors in Japan are known to prescribe the highest amount of medicines in the world.
There have been earlier researches which indicated a few cases of resistance to Tamiflu in type A flu. This type of flu is most likely to cause a pandemic if bird flu changes into a form that is more easily spread among people, not just poultry.
The latest findings, which are published in Wednesday's Journal of the American Medical Association, collected virus samples from patients at four community hospitals in Japan.
It was found that the rate of resistance to Tamiflu is less than 2 percent and also lower than had been found previously in type A influenza. Rates of drug-resistant type A virus have been reported as high as 18 percent.
