With the F.D.A.’s authorization of a coronavirus vaccine on Friday, the United States became the third highly developed Western country — after Britain and Canada — to approve such a drug.

But the three countries have different health care systems and face different challenges in the race to get the vaccine to millions of people. Here are some similarities and differences:
Is it the same vaccine?

For now, yes.

The first vaccine authorized by American regulators, and their British and Canadian counterparts, is the one developed by Pfizer and BioNTech.

But several other vaccines are close behind, particularly one developed by Moderna and the National Institutes of Health, and another from AstraZeneca and the University of Oxford. It could well be that half a dozen or more vaccines are approved in the coming months.
How centralized is the rollout?

In Britain, very. In the United States, not. In Canada, somewhere in between.

With a strong central government and a National Health Service that covers all of its people, Britain is directing the process from London. The national government chose 50 hospitals that would initially get the vaccine and made sure they were prepared; decided how much each one would receive; and drafted rules determining what order people would be eligible to get it.

In the U.S., the federal government is having the vaccine distributed to each state based on population. It will be up to states to decide how to divide the doses among hospitals, clinics and, ultimately, drugstores and doctors’ offices.

Canada has a universal health care system, but it is decentralized, administered by provinces and territories. For vaccine distribution, the central government plans to work through those regional governments. Ottawa will play a large role in directing the process.
How many people will get it at first?

That remains a bit murky.

Canada ordered enough of the Pfizer-BioNTech vaccine for all of its people, Britain enough for 30 percent and the United States enough for 15 percent. But those numbers reflect deliveries that are expected to take months to complete, and Pfizer, like other companies, has hit snags in ramping up production.

All three countries made advance purchases from other companies, as well, so the pace of vaccine approval could significantly affect the speed of rollout. That speed will also be affected by the need for vaccination sites to be equipped with the right freezers, staff, and enough syringes and protective gear.

Initial shipments are a fraction of the pre-purchases — 800,000 doses to Britain and an expected 249,000 this month to Canada. U.S. officials said they hoped to have 40 million doses of the vaccine by the end of the month, which may be optimistic.

In Canada, the government is sending shipments to all 10 provinces. The three northern territories will have to wait. In America, FedEx and UPS will ship vaccines from distribution centers to every part of the country.
How fast will most people get vaccines?

That is even murkier.

Britain, Canada and the United States have followed similar strategies, pre-ordering huge numbers of doses — more than enough to inoculate everyone — from multiple makers, hedging their bets in case some of the vaccines are not approved or some manufacturers have production breakdowns.

Relative to their populations, the United States has ordered far fewer doses than Canada or Britain, and last summer it passed up an offer to increase its advance order from Pfizer. Administration officials say the numbers are misleading, because the government has signed options to buy far more of the vaccine if it sees the need.

But in the face of intense global demand, it is not clear how fast pharmaceutical companies will be able to fulfill the orders they have, much less any additional orders.

In other global developments:

In Brazil, the number of people unwilling to take any Covid-19 vaccine has grown to 22 percent, up from 9 percent in August, Reuters reports. President Jair Bolsonaro, a virus skeptic who has continued to critique coronavirus restrictions, said he would not take a coronavirus vaccine. He has been particularly skeptical of China’s Sinovac vaccine. In November, Brazil suspended a late-stage trial of the vaccine. Although Brazil’s cases fell during the fall, there’s been an uptick since early November. It’s now averaging about 43,000 cases a day, about double from a month ago.

Brittanya Karma, a Vietnamese-German rapper and reality television star, died on Nov. 29 in Hamburg, Germany, where she was born and lived. She was 29. The cause was complications of Covid-19, her agent said.

Rizieq Shihab, a radical Indonesian cleric who held large gatherings and called for a “moral revolution” after his return from Saudi Arabia last month, surrendered to the police on Saturday on charges of violating coronavirus protocols. Upon his return, Mr. Rizieq, 55, invited 10,000 people to his daughter’s wedding. Authorities said six of his bodyguards were killed by the police in self-defense. In surrendering, he said he would cooperate with the investigation.

— Richard Pérez-Peña, Richard C. Paddock, Dera Menra Sijabat and Christopher F. Schuetze The New York Times