CDC investigates first human cases of new bird flu strain

A new strain of bird flu has killed four people in China and sickened at least seven others, according to Chinese media reports. Chinese health officials blame a new strain of H7N9, an influenza virus detected in birds, but never before seen in humans.

Officials at the U.S. Centers for Disease Control and Prevention are monitoring the situation, but they say it's too early to recommend any precautions for the general public.

"While cases have been seen of human infections with this virus in China, we haven't seen any cases in the United States or indeed in any country outside China so far," said Dr. Joseph Bresee, chief of the Epidemiology and Prevention Branch of the CDC's Influenza Division.

Although this new strain of H7N9 can apparently spread from birds to humans, there are no confirmed cases of human to human transfer.

Nevertheless, flu viruses always pose a threat of mutating into something more contagious. So, as a routine precaution, steps are already underway toward developing a vaccine should it be needed.

"We started that process now, and we can stop it if it turns out this virus doesn't pose a threat worthy of vaccine production," Bresee said. "But it's good to get it started as early as you can because vaccines may take a long time to make."