( CNN ) -- Two more people in China have died from the H7N9 bird flu virus , raising the country 's death toll to five , state-run news agency Xinhua reported Thursday , citing Shanghai health officials . H7N9 is a strain of avian flu not detected in humans before China 's recent cases , which the country began reporting on Sunday . Fourteen human cases of H7N9 -- all in eastern China -- have now been reported , according to Xinhua . `` We do n't know yet where the humans got their virus from , '' said Dr. Joseph Bresee , who heads the epidemiology and prevention branch in the Centers for Disease Control and Prevention 's influenza division . The virus has not been shown to spread easily between humans , he added . The two most recent deaths happened Wednesday in Shanghai hospitals . All but one of the five deaths have occurred in that city . One of Wednesday 's deaths was that of a 48-year-old poultry transporter who , although he died in Shanghai , lived in nearby Jiangsu province , Xinhua reported . The three previously reported deaths were : two men -- ages 27 and 87 -- who lived in Shanghai , and a 38-year-old man who lived in Zhejiang province but worked in Jiangsu province , according to state-run news agency Xinhua . The CDC 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 Miriam Falco contributed to this report .
Source : China , says agency working with Chinese to find source . Two people died of H7N9 flu on Wednesday in China , state - run news agency reports . All of the day 's 14 cases were reported in eastern China . H7N9 is a strain of avian flu not previously detected in humans .