Vaccine updates: Majority of Riverside County could be vaccinated 'by late summer' As COVID-19 vaccine supply ramps up in the U.S., one Riverside County official predicts the majority of the region could be inoculated by the fall. "My best guess is that by late summer, we will have had enough supply to vaccinate the majority of our population in Riverside County," Dr. Geoffrey Leung, Riverside University Health System-Medical Center chief of family medicine, said during a Board of Supervisors meeting Tuesday. Riverside County has administered more than 500,000 total doses so far, Leung said. The county is home to a population of 2.5 million.