State media reports in China say the death toll from a new strain of bird flu has risen to nine.
The official Xinhua news service on Tuesday quotes authorities as saying a vaccine should be ready within months.
The World Health Organisation has said it is looking into two suspected "family clusters" of people in China who may be infected with the H7N9 virus - potentially the first evidence of human-to-human spread, Reuters reports.
The H7N9 strain was confirmed in humans for the first time in February this year is severe, leading to fears that if it becomes easily transmissible, it could cause a deadly influenza pandemic.
The latest victim was from Anhui province, Xinhua reports. The strain has now infected 28 people, all in eastern China and nine have died, according to data from the National Health and Family Planning Commission cited in the Xinhua report.
The cases include another four people confirmed to be infected with the virus - two in Shanghai and two in Zhejiang province, one of whom was dangerously ill, according to Xinhua.
The China Securities Journal reported on Wednesday that a vaccine for H7N9 has been authorised by China Food and Drug Administration and is expected to be introduced to the market in the first half of this year.
The exact source of infection remains unknown, although samples had tested positive in some birds in poultry markets that remain the focus of investigations by China and the United Nation's Food and Agriculture Organisation.
