In the past 10 years, a deadly strain of bird flu has killed more than half of the people who got it. Now, there's a new strain of bird flu circulating that can kill about a third of the humans who contract it. Whenever there's a virus this lethal, there are always fears of a pandemic.
Several years ago, men in protective suits decontaminating poultry farms and destroying chickens infected with a deadly bird flu was a scene witnessed throughout Asia. The virus killed birds, and although it rarely infected people, those who got it were more likely to die than to recover.
That virus was H5N1. There's now a vaccine against it for poultry.
But a new strain of bird strain has emerged and is causing alarm. This one is called H7N9. H7N9 doesn't kill poultry or even make them sick, but it can be deadly when it is transmitted from a chicken to a person.
One concern that's been raised is that every time a human gets the H7N9 virus, the world is closer to a pandemic.
"That’s not correct," said Anthony Fauci, who heads the infectious diseases division at the National Institutes of Health.
"Microbes continue to emerge and re-emerge. The concern about this is that these viruses have jumped into humans and have been lethal. The news that is somewhat comforting is that it hasn’t had sustained transmissibility," Fauci continued.
Because of the genetic makeup of these strains of bird flu, it is difficult for them to spread from person to person. Since the H7N9 virus emerged a year ago, some 350 people have caught it. Thirty percent have died. Most had contact with poultry.
"There’s always the danger when you have influenzas that infect chickens, that when you have the close quarters of chickens spreading from one to another and occasionally a human coming into close contact, that there will be the jumping of species from a chicken to a human. This is not something new," said Fauci.
Fauci said any time a new virus emerges, health officials have to watch it carefully. The U.S. has developed a vaccine for H5N1 and is working on one for the newer strain of bird flu, but he doesn't think this new strain is any more threatening than H5N1. This virus has been circulating since 2003 and still doesn't spread easily from person to person.