China's bird flu death toll rises to 6 as researchers seek vaccine April 5, 2013 -- Updated 0613 GMT (1413 HKT) Fourteen cases of H7N9 have been reported in eastern China so far The strain of bird flu hadn't been reported in humans before those cases No cases of human-to-human transmission virus have been confirmed But a person who had contact with a deceased patient in Shanghai shows flu symptoms Hong Kong (CNN) -- A sixth person in eastern China has died from an unusual strain of bird flu, Chinese health authorities said Friday, as researchers in the United States work on developing a vaccine for the virus. No cases of human-to-human transmission of the H7N9 virus have been confirmed so far, but Shanghai authorities said late Thursday that a person who had close contact with a patient who died of the virus was being treated in quarantine after showing symptoms of fever, runny nose and itchy throat, China's state-run news agency Xinhua reported. A 64-year-old man died Thursday night in Huzhou, Zhejiang province, the provincial health bureau said Friday. He died hours after doctors had confirmed he had been infected with the H7N9 virus, it said. He is one of the 14 human cases of H7N9 reported so far -- all of them in eastern China. The H7N9 strain of bird flu had not been detected in humans before the recent Chinese cases, which authorities began reporting on Sunday. Four of the deaths happened in Shanghai, the two others in Zhejiang. "We don't know yet where the humans got their virus from," said Dr. Joseph Bresee, who heads the epidemiology and prevention branch in the U.S. Centers for Disease Control and Prevention's (CDC) influenza division. The CDC, based in Atlanta, is working closely with Chinese authorities trying to find the source of the human infections, Bresee said. "There are lots of things happening at CDC to prepare for this virus," Bresee said. "State health departments are readying themselves just in case," and researchers are working on developing a vaccine for this strain, he said. CNN's Feng Ke in Beijing contributed to this report.