More than three dozen volunteers received multiple, intravenous doses of a vaccine produced with a weakened form of the disease, scientists from the National Institutes of Health, the Navy, Army and other organizations reported Thursday.

Though the results were promising, more extensive field testing will be required, the researchers wrote. Nevertheless, the it marks the first time any vaccine trial has shown 100% success in protecting subjects from the mosquito-borne tropical disease, which sickens more than 200 million a year and killed about 660,000 in 2010.

Dr. William Schaffner, head of the preventive medicine department at Vanderbilt University's medical school, called the results "a scientific advance" -- but cautioned that it's "not ready yet for prime time."