Tracking the pandemic in the US In late 2020, the coronavirus pandemic entered its deadliest phase yet in the United States. As colder weather took hold and the holidays arrived, the nation set repeat records for new... AP NEWS

ALSO SEE: How Is The COVID-19 Vaccination Campaign Going In Your State?

In late 2020, the coronavirus pandemic entered its deadliest phase yet in the United States. As colder weather took hold and the holidays arrived, the nation set repeat records for new infections and deaths.

December was by far the most lethal month, but it also brought hope: Precious vaccines arrived offering the potential to contain the disease in the near future.

The shots got off to a slow start. Initially, they went to health care workers and nursing home residents. Those 75 and older were next in line. But problems arose in vaccinating even that limited pool of people. Some hospital and nursing home workers were hesitant to get the vaccine. Scheduling issues created delays in getting shots to nursing homes. Politicians and health officials complained that too many doses were sitting unused on shelves.

So barely a month into the largest vaccination campaign in U.S. history, the nation shifted gears to speed the delivery of shots. The government decided to stop holding back required second doses of the Pfizer-BioNTech and Moderna vaccines, practically doubling supply. States were advised to start vaccinating other groups lower down the priority scale, including people age 65 and older, and younger people with certain health problems.