Tested in mice, the antibodies work by binding to a previously obscure structure in the flu virus which, when blocked, sabotages the pathogen's ability to enter the cell it is trying to infect, according to the study.
Because this structure -- described by one scientist as a "viral Achilles' heel" -- is genetically stable and has resisted mutation over time, the antibodies are effective against many different strains.
The breakthrough "holds considerable promise for further development into a medical tool to treat and prevent seasonal as well as pandemic influenza," said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, which helped fund the study.
Seasonal flu kills more than 250,000 people every year, and pandemic flu, which occurs with the emergence of deadly viral strains against which people lack immunity, remains an ever-present threat.
Vaccines have long been the first line of defense against flu, but even seasonal viruses evolve so rapidly that the vaccines need to be updated every year. Even then, they are not always effective.
Marasco and colleagues turned up 10 of the artificial antibodies that bound to the H5N1 avian flu, said the study, published in the Nature Group's journal Nature Structural and Molecular Biology.
In further experiments with mice, the scientists found that three of these monoclonal antibodies neutralised 10 of 16 known influenza "A" viruses, including H5N1.
To date, only persons in close contact with infected fowl have become infected with this deadly strain. But scientists fear that a future mutation could "jump species" and become easily transmissible among humans.
These were startling results. Not only had a single type of antibody honed in on different strains of virus, it had disarmed the pathogens on its own without having to call in immune system reinforcements.
In a commentary, also published by Nature, Taia Wang and Peter Palese of the Mount Sinai School of Medicine in New York said the study had uncovered "a viral Achilles' heel" that is resistant to genetic variation.
The new findings "brings us closer to the development of a universal influenza virus vaccine," they said.