Vietnam has started clinical trials for developing a human vaccine for the H5N1 virus, researchers said in the country that has recorded 52 deaths from bird flu. Eleven volunteers, all researchers, received their second dosage of the trial vaccine on Thursday inside spotlessly-clean medical rooms of a company run by the National Institute of Hygiene and Epidemiology in Hanoi. Dr Nguyen Tuyet Nga, the epidemiologist and virologist heading the trial, said experts were using the highly-pathogenic strain of H5N1 taken from humans in Vietnam and known as VN1194.