Trucks carrying Johnson & Johnson ’s newly authorized Covid-19 vaccine began rolling out Monday en route to states and sites that have been seeking more doses to boost vaccinations.

McKesson Corp. , which is serving as the centralized distributor for J&J vaccines, is working with FedEx and UPS to ship the doses nationwide. The shipments are expected to reach states and vaccination sites as early as Tuesday, the Biden administration said.

A FedEx Corp. spokeswoman said pickups had begun at a McKesson facility in Olive Branch, Miss. The shipping company is using its distribution hub in Memphis, Tenn., to deliver the doses nationwide.

UPS trucks picked up J&J vaccine from a McKesson facility in Shepherdsville, Ky., on Monday and brought them to a UPS center in Louisville, Ky., a United Parcel Service Inc. spokesman said. The doses will then be flown to UPS sites throughout the country for delivery by vehicle Tuesday morning.

The U.S. Food and Drug Administration on Saturday authorized use of the J&J vaccine. The drug company had made nearly four million doses for initial shipment. The administration said it expects about 20 million doses to be delivered by the end of March.