Nearly 75% of previously uninsured Massachusetts residents now have medical coverage under the state's campaign to extend health insurance to virtually everyone, according to a report. Since the program's launch in June 2006, 439,000 more people have enrolled in health insurance, and nearly half of them signed up for private insurance not funded by taxpayers. Before 2006, it was estimated that about 600,000 Massachusetts residents lacked health insurance. The expansion has spurred a substantial drop in patients seeking routine care in hospital emergency rooms, and the reduction is already saving the state millions of dollars, according to the report.