The annual flu season has gotten off to an early start with an aggressive variant of influenza, a large and early outbreak of norovirus or "stomach flu," and the worst outbreak of whooping cough in 60 years, with 42,000 confirmed cases. The flu outbreak is one of the worst in more than 10 years, leading to a shortage of the vaccine and Tamiflu treatment for children. “At this point we are not able to make any more vaccine because we are gearing up for next year's vaccine,” said a spokesman for Sanofi, one of the largest manufacturers of the flu vaccine. Boston’s mayor has declared a public health emergency due to widespread cases in the state. On a national scale, deaths and hospitalizations are still below epidemic thresholds, but experts believe that will change.