BOSTON (CBS) — Tufts Medical Center and Boston Medical Center have both received their first shipment of the Johnson & Johnson coronavirus vaccine. The single-dose shot was just authorized by federal regulators for emergency use over the weekend.

Tufts and BMC both said they received 2,000 doses. Tufts will start administering the shots at its COVID-19 vaccination clinic on Thursday, and BMC said it will do the same for patients “later this week.”

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It’s not clear when the first doses will start to be administered throughout Massachusetts. Gov. Charlie Baker had said Monday that the state expected to receive its first shipment of the vaccine next week and the distribution plan for the immediate future remains “a little bit up in the air.”

Johnson & Johnson currently has four million doses ready to go. The company plans to have 20 million more made by the end of March and 100 million by the end of June.

President Joe Biden is expected to announce Tuesday that Merck will work with Johnson & Johnson to manufacture the single-shot vaccine.

The governor has called Johnson & Johnson a “game-changer” in recent months because it is one dose, and does not need require a deep freeze.

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Visit Mass.Gov/CovidVaccine to find out when you’re eligible and to book an appointment or call the hotline at 211.

CBSBoston.com Staff