Health officials say this year’s flu outbreak is the worst in a decade, and Boston on Wednesday declared a public health emergency as the flu epidemic worsened. Forty-one states are currently experiencing widespread flu activity, and Massachusetts is one of 29 states reporting high levels of flu-like illness. We asked Mark Douglass, an associate clinical professor of pharmacy in the Bouvé College of Health Sciences, how people can protect themselves from the flu and why they should get vaccinated if they haven’t already.