The first human antibody that can knock out all influenza A viruses has been shown effective in lab mice, an exciting step forward in the hunt for a universal vaccine, researchers said Friday.

The broadly neutralizing antibody, called FI6, could help vaccinate people against the flu without scientists struggling to piece together a new cocktail each season to match the often-changing strains.

Antonio Lanzavecchia, lead author of the study published this week in the US journal Science, described the finding as "significant," but noted it may be five years before it can be made into a widely available treatment.

"The antibody works not only by neutralizing the virus, which we knew, but also by recruiting killer cells to the virus-infected cells," Lanzavecchia, director of Switzerland's Institute for Research in Biomedicine, told AFP in a phone interview.

"This suggests that once tested in a human system, the antibodies should work even better."

The antibody was found in plasma cells from a human donor. When given to mice heavily dosed with flu viruses, it was able to knock out the illness, offering hope for use as a remedy in people who get infected with the flu.

The discovery was made by using newly patented technology to screen hundreds of thousands of plasma cells in order to isolate the rare ones that produced the antibody.

"We are convinced that this is a very rare specificity but it is a very potent antibody," said Lanzavecchia, who is also chief scientific officer at patent-holder Humlabs.

"The method was really the key to get this very rare antibody."

The antibody was tested in all 16 subtypes of A flu viruses and consistently worked against the often-changing hemagglutinin (HA), the protein that is on the virus's surface.

Mice and ferrets recovered from what would have otherwise been a lethal dose of flu virus when they were given the antibody within two days of infection.

British virologist John Skehel, at the Medical Research Council's National Institute for Medical Research at Mill Hill, said the finding may eliminate the need to combine different antibodies into a single shot against the flu every season.

"In terms of designing a vaccine, the main advantage of this completely cross-reactive antibody is that you can focus on the region of HA recognized by one antibody, rather than having to piece together structures from different antibodies," Skehel said in an email.

"In terms of therapeutic use, progress may be quicker, and will move toward clinical trials of the antibody very similar to those required before use of anti-viral drugs."

Flu pandemics are unpredictable, and millions of people around the world are infected annually with seasonal flu varieties that can be lethal for those with weak immune systems, including children, the elderly and pregnant women.

The spread of A(H1N1), or "swine flu," killed at least 18,449 people and affected some 214 countries and territories after it was uncovered in Mexico and the United States in April 2009.

The World Health Organization declared a pandemic on June 11, 2009. The event was formally over on August 10, 2010.

Lanzavecchia said "unpredictability of new pandemics highlights the need for better treatments that target all influenza viruses."

The next steps are to try to develop the antibodies into a treatment for flu-infected people, while scientists use the findings to work toward developing a vaccine that could coax the body into producing such antibodies.

"We have a low-hanging fruit, which is the antibody itself and the potential use of the antibody as a drug," he said.

"Then we have the long-term project, which is the use of the information obtained from the antibody to make a vaccine."

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