Roughly 71 percent of employees at acute care hospitals in Massachusetts received flu vaccinations last season, according to a report released yesterday by state public health regulators. The percentages have increased since the 2008-2009 season, but not nearly to the levels regulators had hoped for. That spurred a debate about mandating vaccines for hospital workers at a meeting of the Public Health Council, an appointed panel of doctors, consumer advocates, and professors. Madeleine Biondolillo, director of the Bureau of Healthcare Safety and Quality, presented a proposal calling on all acute care hospitals to aim for an employee vaccination rate this flu season of greater than 90 percent and no lower than 73 percent.