1918 and 2009 viruses share vulnerability

BETHESDA, Md., March 24 (UPI) -- U.S. scientists say they've found the viruses that caused flu pandemics in 1918 and 2009 share a structural detail making both susceptible to neutralization.

In one experiment, the researchers, led by Dr. Gary Nabel of the National Institute of Allergy and Infectious Diseases, injected mice with a vaccine made from inactivated 1918 influenza virus. Then they exposed the mice to high levels of the 2009 H1N1 virus. All of the vaccinated mice survived.

But the reverse was also true. Mice vaccinated with inactivated 2009 H1N1 virus and then exposed to the 1918 virus were protected.

"This is a surprising result," Nabel said. "We wouldn't have expected that cross-reactive antibodies would be generated against viruses separated by so many years."

The researchers subsequently determined both viruses lack a cap of glycan (sugar) molecules. Without the sugars, both viruses have unfettered access to receptors they use to enter human cells. That viral advantage quickly diminishes as immunity provided by neutralizing antibodies arises in people who have been infected and recovered or when people are vaccinated.

"The glycans act like an umbrella that shields the virus from the immune system," Nabel said. "They create a physical barrier over the virus and prevent antibody neutralization."

Nabel said the shared vulnerability might be exploited to design vaccines matched to future pandemic influenza virus strains.

The research appears in the early online edition of the journal Science Translational Medicine.