The Danbury Health Department is urging residents to get a flu shot.  This season, all flu vaccines will be designed to protect against the four flu viruses that research indicates will be most common.  Officials say everyone 6 months and older should get an annual flu vaccine, ideally by the end of October.  The CDC says vaccination is important for health care workers, and other people who live with or care for people at higher risk to keep from spreading flu to them.