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."

Boston is believed to be the first city to embrace this particular approach to tracking vaccinations against the seasonal flu, estimated to kill 36,000 people each year in the United States, principally the elderly.

But when Boston bought the monitoring system from a Milwaukee company in 2006, emergency authorities had a far different use in mind: tracking people injured in

Its about tracking and keeping tabs on people full stop.