"In some of the viruses they have isolated in humans, these viruses could attach to either avian or human receptors," he says. "The implication of this is that it's as if the virus is slowly adapting and learning how to expand its host range. This is very bad news indeed for humans."
Aside from the implications of the research as an early warning tool, some experts say it offers a glimpse at how close we are to a pandemic.
"By analogy, the current H5N1 virus is like an enemy that possesses a nuclear device, has the intention of using the nuclear device, but does not have a delivery missile," Hinrichs says. "When all three are present, the enemy becomes fully capable, and we must increase our readiness to respond."
So far, not a single case of human-to-human transmission of H5N1 has been recorded. Also, the United States remains apparently untouched by H5N1, as no human or bird cases have yet been reported in the country.
"This shouldn't change the current pandemic threat situation, so there is no cause for added anxiety," Hayden says. If anything, he adds, the research taking place now could give agencies like WHO the upper hand in containing a potential pandemic before it has the chance to spread.
"It should be emphasized that this research does not indicate that the current H5NI bird virus has acquired these mutations," Hinrichs says. "The research adds to our knowledge by identifying the location of where changes in the virus could occur that would allow it to pass from human to human."
And in the fight to stem a pandemic, knowledge is a crucial weapon.
"These findings have an indirect implication for development of viral vaccines in that the target sites for the vaccine may incorporate the sites of the new mutations," Hinrichs says.
This means that those working to develop vaccines to fight H5N1 could use the newly discovered mutations to their advantage, exploiting the differences that set the human-infecting viruses apart from the crowd.
But Poland says research cannot keep pace with the accelerating changes in H5N1 and other potentially pandemic strains.
"Take 'if' out of your vocabulary. We absolutely, positively -- I will stake my life on it -- have a pandemic," Poland says. "No one knows when, how severe it will be, or what virus it will be. But what we can say is that the leading candidate right now is the H5N1 virus."