Study: H1N1 flu spreads inefficiently

BOSTON, July 3 (UPI) -- Influenza A H1N1, the swine flu virus, has so far spread from person to person less effectively than other seasonal flu viruses, U.S. researchers found.

A team at the Massachusetts Institute of Technology and the Centers for Disease Control and Prevention says the virus has a form of surface protein that binds inefficiently to receptors found in the human respiratory tract.

"While the virus is able to bind human receptors, it clearly appears to be restricted," lead author Ram Sasisekharan, director of the Harvard-MIT Division of Health Sciences and Technology, said in a statement. "We need to pay careful attention to the evolution of this virus."

Sasisekharan said the restricted, or weak, binding, along with a genetic variation in an H1N1 polymerase enzyme, explains why the virus has not spread as efficiently as seasonal flu. However, flu viruses are known to mutate rapidly, so there is cause for concern if H1N1 undergoes mutations that improve its binding affinity.

In the Science paper, Sasisekharan, CDC senior microbiologist Terrence Tumpey and colleagues compared the new H1N1 strain to several seasonal flu strains, including some milder H1N1 strains, and to the virus that caused the 1918 flu pandemic.

The team found that the new H1N1 strain's binds human receptors much less effectively than other flu viruses that infect humans.