Columbia/Boone County Public Health and Human Services will host a walk-in flu vaccination clinic Wednesday from 3:30 until 6 at the Hallsville Community Center. No appointments are needed. The flu vaccine will be available to all residents aged six months and older, with those 18 and under getting them at no cost thanks to MU Health Care. The cost of the vaccine for adults varies depending on insurance coverage. For self-pay residents, the cost is 25 dollars. A high-dose flu shot is available specifically for those 65 and older.