A new study of 45000 humans in Vietnam has revealed that up to 750 cases of human infection of the dreaded H5N1 bird flu virus. The Stockholm based Karolinska Institute's study says that the potential number of victims could run into the thousands. Doctors had estimated that the bird flu will die, but the study shows that hundreds of thousands of people may be infected but with only minor symptoms. Since they do not admit themselves or seek professional help, it is likely that these cases do not end up in Government statistics. Reporting the study in the Archives of Internal Medicine, the scientists say that the transmission to virus may be more frequent that thought earlier. University College London Professor Peter Dunhill, believed to be an expert on bird flu, says that it is likely that the population in Vietnam and even Turkey, living with the virus for over a decade, may have developed an immunity to this disease over time. However, European nations with no exposure to this virus may be facing a major threat and threat of epidemic higher.