United Center Mass Vaccination Site Vaccinations are expected to begin on March 9 at a new mass vaccination clinic at the United Center in Chicago. With up to 6,000 doses per day expected once the site is up and running. Appointments are scheduled to open at 8:30 a.m. on March 4, but only for Illinois residents age 65 and older. The senior-only appointment window will continue through 4 p.m. March 7. Illinois residents have two options for making appointments: online and through a call center. To register online, visit Zocdoc.com/vaccine. The web site is projected to handle much higher volume of appointment requests. Zocdoc will show real-time appointment availability and eligible residents will then be able to select a date/time and book an appointment online. Date of birth will be required when booking an appointment to confirm vaccine eligibility.