Something extraordinary, and extraordinarily rare, happened in the wee hours of April 25: The world administered its 1-billionth-plus dose of a COVID vaccine. Reaching such a milestone in just more than a year of a global pandemic is unprecedented and the fruits of an immunization campaign the likes of which we've never seen before. Creating vaccines this quickly is an impressive feat in and of itself, but nearly 13% of the world's population actually getting vaccinated is arguably an even more impressive accomplishment given the practical roadblocks.

To be clear: This doesn't mean about an eighth of the entire world has been fully vaccinated. It just means that many doses have been administered, whether as part of a one-dose or two-dose regimen.

But stark geographical differences remain, resulting in a lopsided vaccine rollout. Depending on which country you're talking about, more than 50% of the adult population may have received at least one shot (as is the case in the U.S.) while nations in Africa or Asia are moving at a significantly slower pace. While high-income nations make up just 16% of the global population, they have administered 47% of COVID vaccine doses to date。

The world at large, particularly developing countries, has been relying on a partnership called COVAX, which incorporates global health players running the gamut from the World Health Organization (WHO) to vaccine alliances such as Gavi.

From how different nations have been coping with their vaccine rollouts to the companies creating jabs that go to different regions, here's where the world stands more than 1 billion doses in.

Which countries have done the best on vaccination?

To date, nations with more advanced economies have made more progress in vaccinating their populations. That's not exactly shocking, given the lack of health care infrastructure in many developing nations and the fact that other countries, usually wealthy, bought up supplies early on.

There are, on average, about 16 million doses being administered per day. But it's important to differentiate the total number of shots in arms in a given country versus the per capita total.

If we focus on fully vaccinated individuals, or those who have received two doses of the vaccines such as Pfizer/BioNTech’s, which require a dual-shot combo, or of a single-dose vaccine such as Johnson & Johnson's, Israel is doing the best with 56% of its population fully vaccinated and 61% at least partially vaccinated, according to the New York Times. Over the weekend, the country achieved the milestone of zero recorded COVID-related deaths two days in a row.

But Israel has a population of about 9 million people and a significantly smaller land mass, on top of a well-heeled initial vaccine rollout. Among the more populous nations in the world, the United States has been moving at an impressive clip, with nearly 229 million doses administered to date and nearly 95 million people fully vaccinated, according to the CDC.

Which countries are struggling with COVID vaccinations?

There are also nations struggling with the vaccine ramp-up. Multiple countries have what results in a statistical zero percent of their residents vaccinated at all.

The bulk of the nations lagging in the vaccination effort spans Africa, the Middle East, and Asia. That includes Bahrain, the Philippines, Vietnam, Pakistan, Nigeria, Zambia, Iran, and Iraq.

Australia has been facing a massive slump in its own vaccination campaign as it pauses AstraZeneca's shot, which it primarily relies on and can manufacture locally, for those under the age of 50. And while India has done relatively well in its vaccination campaign, last-mile problems have made it difficult to get the numbers up on a per capita basis. The densely populated nation is now facing a massive COVID crisis, with 330,000 new cases detected on April 23 alone.

The most-used COVID vaccines around the globe

Just three COVID vaccines, from Pfizer/BioNTech, Moderna, and Johnson & Johnson, are FDA-authorized in the U.S. But around the globe, there are currently 110 COVID vaccine candidates with 14 approved, according to the COVID-19 Vaccine Tracker.

As the example of Europe's and Australia's chaotic vaccine rollout has underscored, the kinds of vaccines a region relies on can dictate the course of their immunization campaigns.

Oxford and AstraZeneca's vaccine, which has faced scrutiny regarding potential blood clotting side effects, is being administered in the most countries by far—135 to be exact. Next comes the Pfizer/BioNTech and Moderna two-dose mRNA vaccines, followed by China-based Sinopharm's jab.

The trend clearly shows regional preferences. Higher-income nations, and especially the United States, have predictably relied on the first authorized vaccines from Pfizer and Moderna, which are manufactured locally. China has gone with its own local player. And Russia has made aggressive pacts to get its Sputnik COVID shot to other countries even though the country itself doesn't have a particularly high percentage of its population vaccinated.

Other nations are relying on vaccines that Americans likely haven't even heard of. The question in the coming months is whether this vaccine diaspora can still lead to global protection against the coronavirus.