Using technology originally developed for mass disasters, Boston disease trackers are embarking on a novel experiment - one of the first in the country - aimed at eventually creating a citywide registry of everyone who has had a flu vaccination. The resulting vaccination map would allow swift intervention in neighborhoods left vulnerable to the fast-moving respiratory illness. The trial starts this afternoon, when several hundred people are expected to queue up for immunizations at the headquarters of the Boston Public Health Commission. Each of them will get a bracelet printed with a unique identifier code. Information about the vaccine's recipients, and the shot, will be entered into handheld devices similar to those used by delivery truck drivers. Infectious disease specialists in Boston and elsewhere predicted that the registry approach could prove even more useful if something more sinister strikes: a bioterrorism attack or the long-feared arrival of a global flu epidemic. In such crises, the registry could be used to track who received a special vaccine or antidote to a deadly germ. Anything you can do to better pinpoint who's vaccinated and who's not, that's absolutely vital," said Michael Osterholm, director of the Center for Infectious Disease Research & Policy at the University of Minnesota. "I wish more cities were doing this kind of thing." When people arrive for their shots, they will get an ID bracelet with a barcode. Next, basic information - name, age, gender, address - will be entered into the patient tracking database. There will be electronic records, too, of who gave the vaccine and whether it was injected into the right arm or the left, and time-stamped for that day.