How transmissible is H5N1 and how do we prepare?

Study shows genetic change isn't simple

Think broadly when it comes to preparedness. Even if H5N1 avian influenza never becomes a wide-spread threat to humans, you still need to plan for a pandemic, public health experts say.

While no one knows the pandemic potential of H5N1, researchers from the Centers of Disease Control and Prevention who tried to make it transmissible through a simple genetic reassortment found that it was not that easy.

Through genetic engineering, the CDC researchers created a hybrid virus of H5N1 and H3N2, which is a common influenza strain in humans. They tested the transmissibility of this new hybrid in ferrets, which are susceptible to human strains, and found that it did not transmit easily.

The genetically engineered virus also was less virulent than H5N1, researchers said.

The tests used a 1997 strain of H5N1 and mirrored the combination of two viruses that occurred in the 1957 and 1968 pandemics. The 1918 pandemic flu virus is believed to have emerged from long-term genetic changes.

"These data do not mean that H5N1 cannot convert to be transmissible from one person to another person," CDC director Julie L. Gerberding, MD, MPH, said in a press briefing. "They mean that it is probably not a simple process and more than simple genetic exchanges are necessary, and that complexity is something that we will be working on in subsequent experiments at CDC.

"We have a lot of work to do to prepare for a pandemic, and whether or not it is an H5N1 pandemic or some other pandemic," she said. "It's absolutely essential that we continue our preparedness efforts."

Pandemic preparedness is a race against time, with no way of knowing when a pandemic might occur or what virus it will be, notes Scott D. Holmberg, MD, MPH, senior infectious disease epidemiologist with RTI International, a Research Triangle Park, NC-based research institute.

"We know that in five years, or in several years, we'll have more and better vaccines and more and better antiviral vaccines," he says. "We don't know how rapidly the virus might mutate into a more lethal or transmissible form."

Meanwhile, the planning can encompass other novel viruses or infectious disease threats. "You should take advantage of the funding to think a little bit outside the box and how you can use that funding to take care of other health care problems," says Deborah Levy, PhD, MPH, senior adviser for health care preparedness at the CDC.