Although some critics have asked why it took so long to publicly announce the outbreak of the H7N9 virus, public health experts have so far commended the government for responsiveness and transparency in the five days since officials identified the first victims.

“It was the Ministry of Health and Family Planning that first came to us and volunteered the information,” said Gregory Hartl, a spokesman for the World Health Organization in Geneva. “Their response has been excellent.”

Health officials around the world are monitoring the outbreak, which has killed nearly half of the 14 people in whom the virus has been diagnosed. What they fear most is that the disease will mutate so that it can spread from human to human; there has yet to be a confirmed case of transmission between humans. However, the state news media on Friday reported that Shanghai officials had placed in quarantine a person with flulike symptoms who had contact with a victim of H7N9.

Experts say the virus appears to respond to existing influenza medications like Tamiflu and Relenza. In the United States, federal health officials on Thursday said they had begun working on a vaccine for H7N9.