People who lived through the 1918 flu pandemic that killed 50 million worldwide are still producing antibodies to the virus 90 years later, researchers report. "Most people have a notion that elderly people have very weak immunity or they have lost immunity," said lead researcher Dr. James E. Crowe Jr., a professor of pediatrics, microbiology and immunology at Vanderbilt University. "This study shows that extremely elderly people have retained memory of being infected with the 1918 flu, even 90 years later," Crowe said. This is the first evidence that shows that people developed significant immunity to the 1918 flu virus, Crowe said. "It's important to know that you can develop immunity to such a pandemic virus. That has implications for new pandemic viruses," he said. The report is published in the Aug. 17 issue ofNature.