Bird flu human-to-human spread unlikely

LONDON, Nov. 20 (UPI) -- Bird flu would need two simultaneous mutations to spread from human to human, British and U.S. researchers say.

The study, published in PLoS One, finds the unlikelihood of two mutations occurring at the same time makes sustained human-to-human transmission less probable.

"Our new research suggests that it is less likely than we thought that H5N1 will cause a pandemic, because it's far harder for it to infect the right cells," corresponding author Wendy Barclay of the Imperial College London says in a statement. "However, viruses mutate all the time, so we shouldn't be complacent. Our new findings do not mean that this kind of pandemic could never happen. It's important that scientists keep working on vaccines so that people can be protected if such an event occurs."

The researchers say H5 strains of influenza are widespread in bird populations around the world and occasionally infect humans. The H5N1 strain has infected more than 400 people since 2003. The mortality rate in humans is at around 60 percent, the study says.