Rivers Casino in Schenectady to host another mass-vaccination clinic Thursday; 1,100-plus doses available | The Daily Gazette SECTIONS Shares0 Schenectady County Public Health Services announced the event Tuesday. More than 1,100 doses of the Pfizer COVID-19 vaccine will be administered from 9 a.m. to 7 p.m. in the event venue at Rivers. Appointments are required. Attendees will be signed up for the second dose of the two-shot vaccine at the same time as they make the appointment for the first dose. The second dose will be 21 days later, also at Rivers. Appointments are available through the county website, www.schenectadycounty.com. Those who need help scheduling an appointment can receive assistance in person at the Karen B. Johnson Library — the main branch at 99 Clinton St. in downtown Schenectady.