Your complete coronavirus vaccine calendar: When Moderna's candidate is likely to get authorized, and when you could receive your Pfizer shot

• Three companies developing COVID-19 vaccines — AstraZeneca, Moderna, and Pfizer — have released positive results from their late-stage trials.
• Pfizer's vaccine received emergency authorization from the FDA on Friday, putting it on track to deliver shots as early as Monday.
• An FDA advisory committee will decide whether to recommend Moderna's vaccine on December 17.
• Here's a timeline of when the leading vaccines could reach the public.

Good news about coronavirus vaccines keeps rolling in.

On Friday, Pfizer's coronavirus vaccine became the first candidate to receive emergency authorization in the US. The day before, an advisory committee to the Food and Drug Administration recommended the shot for widespread use in peoples ages 16 and older.

Moderna's shot could be next: The company applied for an emergency use authorization (EUA) from the FDA on November 30. From there, an FDA advisory committee will determine if the vaccine meets their recommendation standards.

But the big question still remains: When can Americans get their shots?

Here are the key milestones ahead before vaccines reach the public

December 14: Americans could start receiving Pfizer's vaccine as early as Monday morning, when the first hospitals, clinics, and public health systems are scheduled to receive their shipments. An advisory committee to the Centers for Disease Control and Prevention has recommended that frontline healthcare workers and residents of long-term care facilities get priority access.

December 17: An FDA advisory committee made up of independent scientific experts will meet to evaluate Moderna's EUA request. The meeting will be streamed on the FDA website and on its YouTube, Facebook, and Twitter channels. Moderna will present its safety and efficacy data, then answer questions. After that, the advisory committee will make a recommendation on whether to greenlight the vaccine.

December 18: The FDA is likely to follow the committee's advice, and the vaccine could be authorized within 24 hours, or perhaps a few days later.

By December 21: Moderna shots might not be available until four days after the FDA advisory meeting, given the time it takes to greenlight and ship the vaccines.

Pfizer and Moderna's 2021 vaccine timeline

Moncef Slaoui, the chief advisor to Operation Warp Speed, has estimated that 20 million Americans could get a COVID-19 shot before the end of 2020. But Pfizer's first shipments only contain 2.9 million doses. People who get these early shots will receive second doses after three weeks.

That means vaccinations for the nation's 21 million healthcare workers and 3 million residents of long-term care facilities could last through January 2021.

Slaoui estimated that the US could immunize 100 million people by the end of February. That would require another 60 million doses to be distributed in January, followed by 100 million in February.

By April, vaccines could start being distributed to young, healthy Americans.

Moderna CEO Stéphane Bancel recently told Business Insider that any American who wants a vaccine should have access to one by Memorial Day. Anthony Fauci, director of the National Institute of Allergy and Infectious Disease, has also said that the general population could have access to shots by late spring and early summer.

But those timelines could vary depending on whether additional vaccine candidates besides Pfizer's and Moderna's get emergency authorization.

AstraZeneca's coronavirus vaccine, developed in partnership with the University of Oxford, was found to be 70% effective on average in late-stage clinical trials with more than 20,000 volunteers in the UK and Brazil. The results varied depending on the dosage: A regimen that included two full doses at least one month apart was found to be 62% effective. When volunteers were given a half-dose, followed by a full dose, the effectiveness rose to 90%.

The company still hasn't concluded its US trial, which was delayed for more than a month, but resumed in October. The more vaccine trials that report success, the sooner shots can be widely distributed to the public.

What about other vaccine candidates?

Operation Warp Speed has purchased 100 million doses of Pfizer's vaccine and another 200 million doses of Moderna's.

Slaoui told Bloomberg in November that the program expects to distribute 400 to 450 million vaccine doses from now through May. "Plan A," he added, is to distribute vaccines from two other companies - AstraZeneca and Johnson & Johnson - to help reach that goal.

Slaoui told Business Insider in October that he expects AstraZeneca and Johnson & Johnson's US trials to produce results in December or January. That could put them on track for authorization this winter. The US has already purchased 100 million doses from each company.

"Plan B," Slaoui told Bloomberg, is to order additional doses from Pfizer and Moderna. Agreements with the companies allow the US to acquire another 500 million doses from Pfizer and another 300 million doses from Moderna should it so choose.

The remaining two vaccine candidates backed by Warp Speed come from Novavax and a Sanofi/GlaxoSmithKline partnership. If the companies have trouble finding enough Americans to join their trials once a Pfizer or Moderna vaccine hits the market, Slaoui told Bloomberg, the trials might recruit volunteers in other countries. Both are expected to release pivotal data about their vaccine candidates in early 2021.

If those two vaccines get authorized - that would most likely happen in the spring - the US is prepared to distribute 100 million doses of each as well.

In a recent NPR interview, Fauci said additional vaccine candidates besides Pfizer's and Moderna's "are going to be essential if we want to get enough vaccine to give to everyone who would need it or want it in the country."

This story has been updated with new information about Pfizer's authorization and Moderna's EUA application. It was originally published on November 25.