U.S. distribution of Moderna Inc’s Covid-19 vaccine began on Dec. 19, with more than 3,700 sites due to start receiving and administering shots as soon as Dec. 21, vastly widening the rollout started by Pfizer Inc.

A panel of outside advisers to the U.S. Food and Drug Administration is expected to endorse emergency use of Moderna Inc.’s coronavirus vaccine during a meeting on Dec. 17, as the nation prepares to roll out a second vaccine.

Pfizer, COVID vaccine

The first days of Pfizer Inc.’s Covid-19 vaccine rollout have seen unexpected hitches including some vaccines being stored at excessively cold temperatures and Pfizer reporting potential challenges in vaccine production, U.S. officials said.

An intensive care unit nurse became the first person in New York state to receive the Pfizer/BioNTech Covid-19 vaccine on Dec. 14, marking a pivotal turn in the U.S. effort to control the deadly virus.

The first shipments of Covid-19 vaccine left on trucks and planes early on Dec. 13, kicking off a historic effort to stop a surging pandemic that is claiming more than 2,400 lives a day in the United States.

The United States hit a record 16 million Covid-19 cases on Dec. 12, with deaths closing in on the 300,000 mark, as millions of doses of a new vaccine were expected to start rolling out across the nation on Dec. 13.

Pfizer, COVID vaccine

The United States authorized the use of Pfizer Inc’s Covid-19 vaccine on Dec. 11, with the first inoculations expected within days, marking a turning point in a country where the pandemic has killed more than 295,000 people.

Pfizer Inc. and BioNTech SE announced that the U.S. Food and Drug Administration authorized the emergency use of the mRNA vaccine, BNT162b2, against Covid-19 in individuals 16 years of age or older.