And the Associated Press reported Monday that Chinese health authorities are also at work on a vaccine against H7N9.
"If there was human-to-human transmission, that would be worrisome," said Horovitz. "[But] even then, we don't know how aggressive or fatal it would be."
Although two of the people who were sickened by the virus had had contact with one another, right now it only "smells like the possibility" of human-to-human transmission, Webby added.
"On the whole, it doesn't look like there's any strong evidence that this thing is really running around rampant," he said.
There's more on H7N9 avian flu at the U.S. Centers for Disease Control and Prevention.
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