The massive campaign to vaccinate the United States against the coronavirus has gotten off to a slower start than federal health officials originally had hoped, but the odds are high that 100 million people will be vaccinated by March, an official said in a call with reporters on Wednesday.

As of Thursday morning, just over 1 million doses of vaccines had been administered out of the 9.5 million doses distributed across the country, according to a dashboard maintained by the Centers for Disease Control and Prevention. The first doses of Pfizer’s vaccine were given on Dec. 14, followed by the first doses of Moderna’s at the start of this week.

In recent weeks, federal officials had said they hoped for 20 million people to get their first of two required shots by the end of this year, though they walked back that target last week. On Wednesday, officials said that the federal government was still on track to make 20 million doses available to states and other jurisdictions by the end of the year, with the final deliveries of those doses coming in the first week of January.

“Exactly how fast the ramp-up of immunizations, of shots in arm, is happening is slower than we thought it would be,” said Moncef Slaoui, the scientific adviser of Operation Warp Speed, the Trump administration’s effort to fast-track the development and rollout of coronavirus vaccines.

“We’re here to help states to accelerate that appropriately,” Dr. Slaoui added.

Gen. Gustave Perna, Operation Warp Speed’s logistics lead, said that the reported figures on how many vaccines have been given likely lag the current number by 72 to 96 hours.

General Perna said that the federal government on Tuesday allocated 4.67 million more doses of vaccines — 2.67 million from Pfizer and 2 million from Moderna — and that states will be able to start ordering them on Thursday. The vaccines would then be delivered next week.

Late last week, the pharmacy giants CVS and Walgreens began a drive to vaccinate tens of thousands of nursing homes and other long-term care facilities across the country. This week, the companies are visiting 238 facilities in 12 states, and next week plan to visit an additional 1,000 facilities in 13 more states, General Perna said.

“We’re getting the vaccines out as fast as they are available,” he said.

— Rebecca Robbins The New York Times