Researchers are reporting that blood donated by four survivors of bird flu seems to harbor a potent protection against the deadly virus.

Scientists have long suspected that culling immune-system molecules from survivors could provide a new therapy for a hard-to-treat strain of bird flu known H5N1.

On Monday, they reported the first results of tests on mice. Health benefits seen in animal studies often do not translate to people.

Antibodies culled from the blood of four Vietnamese bird flu survivors using a type of cell known as memory B were injected into mice infected with the flu strain at a U.S. lab, while other infected mice were given antibodies from a non-flu sample.

The mice in the second group became infected and died within a week, while the mice receiving the flu strain antibodies were apparently protected. Researchers found far lower amounts of the virus in the treated mice, and virtually none outside the lungs.

Researchers hope the work will eventually lead to stockpiles of antibodies that could be used during a flu pandemic.

The work was reported in the online journal PLoS-Medicine.