Injections of the newly authorized Moderna vaccine are now underway in the U.S.

In Boston, health care workers at the East Boston Neighborhood Health Center were among the first people to receive Moderna's vaccine. Dr. Jaime Gallegos, the first staffer to get the vaccine, held a sign that said, "Take that, COVID!"

The first cases containing the Moderna vaccine -- which was authorized by the FDA on Friday -- were seen Sunday morning being rolled out from a facility in Olive Branch, Mississippi, to be shipped to the FedEx hub in Memphis, Tennessee, for nationwide distribution.

The doses were packed into insulated coolers with specialized cold packs and a temperature monitor, according to pharmaceutical distribution company McKesson.

ABC News’ Arielle Mitropoulos contributed to this report.

The European Commission authorized the Pfizer vaccine on Monday, hours after the European Medicines Agency issued a recommendation granting a conditional marketing authorization (formal authorization) for the vaccine.

"It will be available to all EU countries at the same time, on the same conditions," tweeted EU Commission President Ursula von der Leyen.

French Prime Minister Jean Castex tweeted, "Vaccination will start in the 27 EU countries on December 27, 28 and 29."

ABC News’ Ibtissem Guenfoud contributed to this report.

The reproduction rate of a new COVID-19 variant linked to an uptick in cases in England is 0.4 higher than other known strains, Dr. Maria Van Kerkhove, the World Health Organization’s COVID-19 technical lead, said Monday.

That means the number of people an infected individual transmits to increases from 1.1 to 1.5 with the new variant.

There’s "zero evidence" that the new variant causes more severe disease, said Dr. Mike Ryan, executive director of the WHO’s Health Emergencies Programme.

The variant was reported to the WHO on Dec. 14. In the last few days, a number of countries have introduced travel bans to the United Kingdom.

The variant has also been identified in one patient in Australia, one in Iceland, one in Italy, one in the Netherlands, and believed to be in about 10 people in Denmark, Van Kerkhove said.

Studies around antibody response are underway. WHO officials said they expect results in the "coming days and the coming weeks."

ABC News’ Christine Theodorou contributed to this report.

Gov. Andrew Cuomo wants New York state added to the list of countries requiring United Kingdom travelers to get tested before flying in the wake of a new variant of the novel coronavirus linked to an uptick in cases in England.

"If 120 countries require testing ... why are we doing nothing?" Cuomo said.

"I know and I believe my intuition is correct that it is another disaster waiting to happen,” Cuomo said.

British Airways and Delta have agreed to the governor’s request to test passengers flying from the U.K. to New York, Cuomo said. Virgin Atlantic is considering the request, Cuomo said.

A number of countries have introduced travel bans to the U.K. France, Germany and several other European countries have suspended flights, while similar measures have been taken around the world -- as far as Canada and Hong Kong.

The New York City health care provider under investigation for allegedly misappropriating the Moderna coronavirus vaccine, told ABC News it will return its vials to the state Health Department.

The New York State Department of Health is currently probing ParCare, which has offices in Brooklyn, to determine if it misused what was an approved allocation toward members of the public not yet prioritized under current New York guidelines.

Under the current state rules, only medical workers, first responders and nursing home staff members are allowed to receive any coronavirus vaccine. Other groups will follow in future rounds.

ParCare touted the vaccine on its social media pages with a flyer that claimed the vaccines would be available on a "first come, first serve basis."

"We have set up a special system where you can reserve your slot. This will enable you to receive the vaccine as soon as it arrives to the center," the flyer said.

The flyer also claimed that the vaccines were only for people who were "elderly," "high risk" or "underlying conditions."

New York state police and other investigators were at the ParCare location in Borough Park on Saturday night.

A spokesman for ParCare told ABC News Sunday evening that it is cooperating with the state investigation and will return its unused vials.

ParCare received 2,300 doses of the Moderna vaccine, and 869 of those doses have already been administered, according to the spokesperson.

"ParCare followed all NYS DOH procedures for obtaining the Moderna vaccine and was approved by NYS DOH for distribution and by CDC as a network site. As a result, we have properly received the vaccines and have provided the documentation regarding the proper receipt of the vaccines to the NYS DOH," the spokesperson told ABC News.

With regards to the patients who received their first shot, ParCare said it will be "working with the state to ensure that we provide the second dose for our patients."

-ABC News' Sasha Pezenik and Aaron Katersky contributed to this report