When and where can I receive the COVID-19 vaccine? The latest: Thanks to an increase in vaccine supply, Missouri will enter Phase 2 of its vaccine rollout plan on Monday, March 29, and Phase 3 (making all adult residents eligible) on Friday, April 9. Editor's note: This guide is regularly updated with the latest information. The latest: Mercy currently has open appointments available to eligible Missourians. Thursday, March 18: Missouri Governor Mike Parson announced in a tweet that "the federal government has informed us that COVID-19 vaccine allotments to Missouri are projected to increase SIGNIFICANTLY by the first week of April." The news means the state can enter Phase 2 of its vaccine rollout plan on Monday, March 29, and Phase 3âopen to all adult residentsâon Friday, April 9.