The new influenza A H7N9 virus has not been seen before in humans, but it doesn’t appear to be transmitted easily among people, and there have been no cases detected in the United States, said Dr. Tom Frieden, the director of the Centers for Disease Control and Prevention.

“There are no specific steps people in this country can take. People can go about their daily lives,” he said.

Still, he said CDC officials are in close contact with Chinese authorities as they track the spread of the novel virus, which has been found in people from four Chinese provinces.

“At this point, there are several things that give us confidence that this is not spreading widely from person to person,” Frieden said.

For example, Chinese authorities have tracked 100 close contacts of people who got sick, and none of them became ill. With typical influenza, perhaps 20 percent to 30 percent of family members could be expected to develop the flu, Frieden said.

CDC is working with vaccine manufacturers to develop a seed strain to produce a vaccine to protect against the H7N9 virus, but that would only occur if there appeared to be widespread transmission. If that were necessary, it would not disrupt production of the seasonal vaccine, CDC officials said.

The agency issued a health alert for U.S. clinicians urging them to be alert for recent travelers from China who could show signs of the novel flu. CDC is also developing a diagnostic test that could quickly detect the virus.

No travel advisories have been issued, but CDC officials are reminding U.S. tourists in China to stay away from live poultry markets. That’s the same advice the agency has issued for about a decade, since outbreaks of SARS and H5N1 flu. The World Health Organization said it was not advising screening at points of entry or any trade restrictions in connection with the outbreak.

China’s neighboring countries are closely monitoring people for signs of flu. A 7-year-old girl in Hong Kong was being tested Friday in a local hospital for signs of the virus, according to the official Chinese news outlet Xinhua. Tougher surveillance also has started in Laos, Cambodia, Thailand and Taiwan, CDC officials said.

Though no source of the outbreak has been identified, Chinese officials have detected the virus in chickens and in pigeons and are now culling flocks to prevent further spread of the virus.

Health officials can’t yet say whether this virus is especially virulent. Wider population tests will need to be conducted to tell whether many people may have become infected with virus without becoming seriously ill, or whether those who got infected developed severe illness.

The virus appears to be common in animals, where it causes only mild illness. Doctors closely monitor cases of animal flu that pass into humans. Seasonal flu kills tens of thousands of people globally every year. But a new virus that starts passing from animals to people could cause far more serious disease.

For instance, H5N1 bird flu kills about 60 percent of the people it infects. But it doesn’t pass easily among people, either, and most of those who’ve gotten appeared to be directly infected by sick chickens.

Still, Frieden noted that flu can mutate very quickly and there’s no way to tell whether this new virus will soon become more transmissible. The H1N1 swine flu in 2009 didn’t cause serious illness, but it spread very quickly. And that bug was a descendant of the 1918 “Spanish flu,” which killed between 50 million and 100 million people worldwide.:

Related stories: 

• Six more diagnosed with new bird flu in China
• New bird flu strain: Little evidence of global threat so far

Source: http://vitals.nbcnews.com/_news/2013/04/05/17618253-dont-panic-over-new-bird-flu-outbreak-cdc-cautions?lite.

By JoNel Aleccia, Senior Writer, NBC News