Boston Mayor Thomas M. Menino declared a public health emergency Wednesday as a result of a massive flu outbreak sweeping across the city of Boston. At least 700 cases have been confirmed, a number up significantly from the 70 confirmed cases at this time last year. Thankfully, the majority of the strains—91 percent—are well matched to a highly effective vaccine. But the worst is far from over. Kevin Cranston, director of the DPH Bureau of Infectious Disease, says the state is off to a “moderately severe” start that is likely to get “more severe” as the weeks go on.