March 10, 2021 at 12:12 pm Mayor Durkan, Governor Inslee, and others announce the opening of mass vaccination site at Lumen Field. (Screengrab from Seattle Channel) The Lumen Field Event Center in Seattle will open as a mass vaccination site on Saturday, March 13. At peak capacity, the Lumen Field site will be the largest civilian-run clinic of its kind in the country. Initially, due to a limited supply of doses, the site will be open two to three days a week and will vaccinate roughly 5,000 people weekly. However, at full supply, Seattle Mayor Jenny Durkan said the site is capable of vaccinating 20,000 people per day.