Avian flu has been at the top of everybody's "hit list" of viruses with pandemic potential for the past decade, Robert Webster, Ph.D., of St. Jude Children's Research Hospital in Memphis, said today at the conference on Influenza Vaccines for the World.
But that changed last week with the emergence of a virus containing fragments from swine, human, and avian viruses, he said.
"H1N1 has come in from left field . . . and stunned us all," he said.
David Fedson, M.D., formerly of the University of Virginia School of Medicine and Aventis Pasteur MSD, now retired, agreed with Dr. Webster.
"We've had no way to anticipate this," he said. "It just shows once again how, if there's anything consistent about influenza virology and influenza virus behavior, it's that you're always going to be surprised . . . and we've been surprised."
Nevertheless, even at number two, H5N1 remains a serious threat, according to John Oxford, Ph.D., scientific director of Retroscreen Virology and a professor of virology at St. Bartholomew's and the Royal London Hospital.
"Just because there's an immediate problem with the swine virus from Mexico, we shouldn't forget H5N1," he said.
Although H5N1 is not easily transmissible between birds and humans, a genetic reassortment could remove that barrier, Dr. Webster said.
The result could be catastrophic considering that, as of April 2009, 61% of the 421 human cases of avian influenza infection have died.
The high death rate is "what scares the bejesus out of us," he said.
Dr. Fedson said that H5N1 "could cause a global population collapse if it developed easy transmissibility and maintained the same virulence characteristics of this virus, which exists in Indonesia, southeast Asia, and other countries. I mean, that is just horrifying to think about."
The avian flu virus has been found in more than 60 countries and has established three epicenters -- in southern China, Indonesia, and Egypt, according to Dr. Webster.
It continues to evolve, as evidenced by the failure of 21 different poultry vaccines against the virus tried in Egypt.
"H5N1 is still alive and well," he said.
Dr. Oxford noted that nobody in the world has an immunity to H5N1, but that most people have been exposed to H1N1 viruses before, although not the newest variation.
Even so, he said that he's sure the previous exposure will at least partially impede the spread of the new virus.
And even though a forecast avian flu pandemic has not yet materialized, the attention the virus garnered when it first appeared could actually help dealing with the current situation.
The avian flu fears led to investment, the building of vaccine production facilities, and government stockpiles of antivirals and other supplies, Dr. Oxford said.
In turn, the current situation with H1N1 "could be a dress rehearsal for something very, very big," he said.
"The [H5N1 avian flu] is the virus most likely to cause a big pandemic, a world shattering affair," he said, "whereas I don't think this swine is going to do that."