Getting the world vaccinated against Covid-19 is a matter of life and death, involving complicated scientific processes, multinational corporations, government promises and backroom deals. So figuring out when and how everyone in the world will get the vaccine is not easy, reports BBC.

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Agathe Demarais is the director of global forecasting at the Economist Intelligence Unit, which has done some of the most comprehensive research on the topic. She has looked at the world's production capacity, along with the healthcare facilities needed to get vaccines into people's arms, the number of people a country has to contend with, and what they can afford.

Many of the findings seem to fall along predictable lines of rich v poor. The UK and the US are both well supplied with vaccines right now because they could afford to invest a lot of money into vaccine development and put themselves at the front of the queue.

Rich countries that didn't do that, like Canada or those in the EU bloc, are a little further behind. Canada was criticised at the end of last year for buying up five times the supply it needs to cover its population, but it seems it wasn't positioned for priority delivery.

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That's partly because the country decided to invest in vaccines from European factories, afraid that the US under Donald Trump would issue export bans. It turned out to be a bad bet. European factories are struggling with supply and recently it has been the EU, not the US, that has been threatening export bans.

"As long as the European market doesn't have enough vaccines, I think that big imports to Canada are going to remain off the cards," says Ms Demarais. Most low-income countries haven't started vaccinating yet. But some countries in the middle are doing better than expected.

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Serbia is eighth in the world in terms of the percentage of its population vaccinated, ahead of any country in the EU.

Its success is partly down to an efficient roll-out but it's also benefitting from vaccine diplomacy - a battle between Russia and China for influence in eastern Europe. It's one of the few places where the Russian vaccine, Sputnik V, and the Chinese vaccine, SinoPharm, are already available.

On paper, Serbians are given a choice of what vaccine they would prefer - Pfizer, Sputnik or SinoPharm. In reality, most people end up being given SinoPharm.

And the influence China is exerting here is likely to be long-term. Countries giving a first and second dose of SinoPharm are also likely to look to China for booster doses if needed.

The United Arab Emirates is also relying heavily on the SinoPharm vaccine - it makes up 80 percent of the doses being administered there right now. And the UAE is building a SinoPharm production facility.

"China is coming with production facilities, trained workers, so it's going to give long-term influence to China," says Demarais. "And it will make it very, very tricky for recipient governments to say no to China for anything in the future."

Being a global vaccine superpower, however, doesn't mean your population will be vaccinated first. The EIU's research predicts two of the world's vaccine production powerhouses, China and India, may not be sufficiently vaccinated until the end of 2022. That's because they have huge populations to contend with, as well as a shortage of health workers.

In India, the country's success as a Covid vaccine producer is largely down to one man, Adar Poonawalla. He's chief executive of the Serum Institute of India, the world's largest vaccine producer.

Last year, his family started to think he has lost his mind when he began betting hundreds of millions of dollars of his own money on vaccines that he didn't know would work.

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In January, the first of those vaccines, developed by Oxford and AstraZeneca, was delivered to the Indian government. Now he's producing 2.4 million doses a day. He's one of two main suppliers to the Indian government - and is also supplying Brazil, Morocco, Bangladesh and South Africa.

'Magic sauce'

"I thought the pressure and all the madness would end now that we've made the product," he says. "But the real challenge is trying to keep everybody happy.

"I thought there'd be so many other manufacturers who would be able to supply. But sadly, at the moment at least, in the first quarter, and perhaps even the second quarter of 2021, we're not going to see a substantial increase in supply."

He says production cannot be ramped up overnight. "It takes time," Ponnawalla adds. "People think that the Serum Institute has got a magic sauce. Yes, we're good at what we do but it's not a magic wand." He currently has an edge because he started building facilities in March last year, as well as stockpiling things like chemicals and glass vials in August.

For manufacturers starting production now, it will take months to produce vaccines. And the same applies to any boosters that might be needed to tackle new variants.

Ponnawalla says he is committed to supplying India and then Africa through a scheme called the Covax facility.

Covax, an initiative lead by the WHO and other health organisations, aims to get affordable vaccines to every country in the world. Countries that can't afford vaccines will get them for free through a special fund. The rest will pay. But the theory is that they will get a better price by negotiating through the bloc than if they had done so on their own.

Covax is planning to start delivering vaccines this month. But the plan is being undermined by the fact many countries involved are also negotiating their own deals on the side.

Poonawalla says almost every leader in Africa has been in touch with him to access vaccines independently. Last week, Uganda announced it had secured 18 million doses from the Serum Institute at $7 a jab - much more than the $4 being paid by Covax. The institute says it is in talks with Uganda but denies this deal was ever signed.

In total, Poonawalla's firm is due to supply 200m doses of the AstraZeneca vaccine to Covax and has promised 900m more doses in the future.

The Africa Centres for Disease Control and Prevention has since advised against rollout of the vaccine in countries where the South African strain is present. He says he is still committed to the scheme, but admits it faces problems. It's dealing with too many different vaccine producers, he says, each offering varying prices and timelines for delivery.

Demarais and the EIU are not overly optimistic about what Covax can achieve either. The timelines for delivery of vaccines are still not clear and even if things go according to plan, the scheme only aims to cover 20-27 percent of a country's population this year. "It's going to make a small marginal difference, but not a game-changer," she says.

In her forecast, some countries may not get widespread coverage even by 2023. Some may never be fully covered. Vaccination may not be a priority for every country, especially one that has a young population and is not seeing huge numbers of people getting sick.

The problem with that scenario is as long as the virus can prosper somewhere it will be able to mutate and migrate. Vaccine-resistant variants will continue to evolve.

It's not all bad news. Vaccines are being produced faster than ever but the scale of the task - inoculating 7.8 billion people around the world - is gigantic. And it's never been attempted before.

Demarais believes governments should level with their people on what is possible. "It's very difficult for a government to say, 'No, we're not going to achieve widespread immunisation coverage before several years.' Nobody wants to say that."