Bird flu H7N9 had emerged in China in 2013 which sparked fears of a global pandemic. Antibodies that protect against bird flu have been isolated in persons receiving seasonal flu vaccinations.

"We have clear evidence that a normal immune response to flu vaccination offers protection against dangerous and highly unique strains of influenza such as H7N9," said co-senior author Patrick Wilson, PhD, associate professor of medicine at the University of Chicago. "We now need to develop ways of amplifying this response."
With a mortality rate of roughly 30 percent, avian influenza A (H7N9) is unusually dangerous for humans. To search for potential therapeutics against the virus, Wilson and his colleagues focused on annual seasonal flu vaccinations. The vaccine causes the immune system to produce antibodies - proteins that bind to and neutralize foreign invaders - against common flu strains.
The researchers studied whether seasonal vaccinations would also induce the production of antibodies against rare flu strains. They selected 83 antibodies - isolated from 28 vaccinated individuals - that reacted with H3N2, a common human flu strain. When tested, seven percent of these antibodies reacted against rare H7 strains, even though H7 strains were not included in the vaccines the subjects received.
Of these, three antibodies appeared to completely neutralize H7N9 avian flu. To verify their findings, the team treated mice with each antibody before exposing them to a lethal dose of H7N9 virus. All three antibodies prevented death in these subjects, compared to controls which succumbed to infection. When the antibodies were tested as a therapeutic and administered 24 hours after infection, mice were again protected.
"It appears more common than previously thought for antibodies induced by flu vaccination to offer cross-protection against H7N9," said study author Carole Henry, PhD, postdoctoral fellow at the University of Chicago. "Although they are not always protective, H7-reactive antibodies can be found in almost everyone that's been vaccinated."
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Despite the efficacy of these antibodies, it is still unclear why they are produced in relatively low amounts. The team is now working to better understand this process and to develop therapeutic approaches based on these antibodies.
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The study, "Preexisting human antibodies neutralize recently emerged H7N9 influenza strains," was supported by the National Institutes of Health, the Gwen Knapp Center for Lupus and Immunology Research and the Center for Research on Influenza Pathogenesis. Additional authors include Paul E. Leon, Kaval Kaur, Gene S. Tan, Nai-Ying Zheng, Sarah Andrews, Min Huang, Xinyan Qu, Yunping Huang, Marlene Salgado-Ferrer, Irvin Y. Ho, William Taylor, Rong Hai, Jens Wrammert, Rafi Ahmed, Adolfo GarcÃa-Sastre, Peter Palese and co-senior author Florian Krammer.
Source-Newswise