Researchers in Japan and the US have analyzed the genes of a new strain of avian (bird) flu that's killed at least 17 people in China in recent weeks, and discovered that some of the new H7N9 viruses have mutated to be more effective and deadlier in humans than they are in birds. The findings "raise concerns regarding their [the virsues'] pandemic potential," according to the researchers, who published their findings in a paper in the journal Eurosurveillance last week.

Specifically, the researchers examined genes from four infected people in China and found that in all cases, the viruses in their bodies lacked certain genes of H7N9 in birds and that "this deletion is associated with increased virulence in mammals," or increased ability to cause illness, and eventually death. By contrast, in birds, the illness caused by these viruses is only relatively mild. Other mutations found from the human virus samples indicated that they preferred to bind with human genes. The research didn't reveal that virus was capable of transmitting between humans directly, which would be major cause for alarm, since avian flu usually only passes from infected birds directly to humans who handle or are in close contact with them. But in China, up to 40 percent of the people infected so far had no direct contact with birds, worrying the World Health Organization.

Still, it's too early to say whether the new viruses will lead to a pandemic, according to the US National Institute of Allergy and Infectious Diseases (NIAID), which funded the new research. “The H7N9 influenza virus is a new concern that the public health and scientific communities will continue to track closely, including watching for any genetic mutations that might enable the virus to become transmissible from person to person or to cause more severe disease,” said NIAID Director Anthony Fauci, M.D. in a statement published online today.

No human cases of the H7N9 bird flu strain have been reported outside of China yet, according to the World Health Organization. Nonetheless, the US Centers for Disease Control and Prevention has ordered a vaccine that's now in development, and several other countries are reported to be making preparations to produce their own, including China and Taiwan, though no official production has begun.