premise: "Tests show that the vaccine is highly safe," said Yin.
  Founded in 2001, Sinovac, known in China as Beijing Kexing Bioproducts Limited Company, focuses on manufacturing and marketing human-use vaccines and related products for infectious diseases such as Hepatitis A and Hepatitis B, influenza and SARS.
  The company was designated to cooperate with the state disease control and prevention center to carry out the research and development for human-use bird flu vaccine, to be used for preventing the disease among humans, since the epidemic among birds was first found in March 2004.
  "We get the virus samples from the lab of the influenza center under the World Health Organization and the research is going on well," said Yin.
  "If the bird flu virus mutates, we can develop new vaccines in four months," said Yin.
   Why might researchers need to develop new vaccines?
hypothesis: the bird flu virus mutates