Antibodies from survivors of the 1918 flu pandemic, the worst in human memory, still protect against the highly deadly virus, researchers reported on Sunday.

The findings by a team of influenza and immune system experts suggest new and better ways to fight viruses -- especially new pandemic strains that emerge and spread before a vaccine can be formulated.

These survivors, now aged 91 to 101, all lived through the pandemic as children.

Their immune systems still carry a memory of that virus and can produce proteins called antibodies that kill the 1918 flu strain with surprising efficiency, the researchers report in the journal Nature.

"It was very surprising that these subjects would still have cells floating in their blood so long afterward," said Dr. James Crowe of Vanderbilt University in Tennessee, who helped lead the study.

The antibodies also protected mice from the 1918 virus, which swept around the world at the end of World War One killing between 50 million and 100 million people, Crowe's team reports in the journal Nature.

"The antibodies that we isolated are remarkable antibodies. They grab onto the virus very tightly and they virtually never fall off," Crowe said in a telephone interview.

"That allows them to kill the 1918 virus with extreme potency, meaning it takes a very small amount of antibody."

The human body has two systems for fighting off bacterial and viral invaders. One system uses so-called T-cells while the other employs B-cells, made in the bone marrow, which in turn make antibodies to both flag and directly attack the targets.


Dr. Christopher Basler and colleagues at the Mount Sinai School of Medicine in New York tested the 1918 survivors and found that in most of them, the B-cells made antibodies highly attuned to the 1918 flu strain.

Dr. Terrence Tumpey at the U.S. Centers for Disease Control and Prevention had worked on a team that resurrected the 1918 virus taken from buried victims of the epidemic and tested this virus in mice. Mice given the antibodies from the elderly survivors lived, while those given placebos died.

Crowe said it will now be important to test other people who have had influenza to see if their immune responses are as strong. "The thought is the first influenza that you see during life is the one that you have the best immunity to," he said.

"If we can learn the rules about how these antibodies work we may be able to design antibodies to lots of other viruses."

The 1918 flu was an H1N1 strain that apparently came straight from birds. "This study tells us that human beings can make long lasting immune responses to bird influenza," Crowe said.

Crowe said his team is working to get antibodies from people vaccinated with experimental shots for the H5N1 avian influenza now circulating in Asia, Europe, the Middle East and Africa. H5N1 mostly affects birds but it has infected 385 people since 2003, killing 243.

Experts fear that, like the H1N1 virus did in 1918, H5N1 will mutate into a form that passes easily among people and spark another pandemic. No one knows if the vaccines being made now would protect against whatever form of H5N1 might emerge.

Crowe said antibodies from survivors might make a good interim treatment while a vaccine is formulated, manufactured and distributed -- a process that would take months.