The stakes are enormous for Geneva-based Gavi and its chief executive Seth Berkley, a US epidemiologist who founded the International Aids Vaccine Initiative. Its own documents reveal an organisation well aware of the risks in taking on the Covid-19 vaccination challenge.

“Failure would cause inequitable access with continued impact on the global economy and Gavi’s core programmes, and may affect Gavi’s reputation,” according to a presentation given by Berkley at a board meeting at the end of September.

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Winning the support of these countries means Covax “lives to fight another day”, said David Fidler, an adjunct fellow with the Council on Foreign Relations in New York. The buy-in is “impressive”, Fidler says, but he has concerns about the extent to which Gavi may have been forced to make trade-offs over the interests of richer countries.

“The problem is that it’s ad hoc within an ad hoc mechanism and there’s not a lot of transparency,” he said. “If Covax is just cutting bilateral deals here and there, at what point does this just become so non-transparent that the political support simply won’t be there when a vaccine shows up, because [countries] don’t know if [they’re] being treated equitably,” he said.

“There is a possibility that this could all just implode,” added Fidler, who was among those calling for a global mechanism for vaccine access after the last pandemic of H1N1 flu in 2009.

But Fidler, like a number of global health specialists, applauds Gavi for stepping forward to combat the familiar pattern in global health emergencies in which rich countries snap up supplies through top-dollar deals, while poorer ones wait for what’s left.

Covax’s primary goal is to deliver enough doses to cover 20 per cent of participating countries’ populations in equitable tranches and on the same timeline, whether they’re rich or poor.

Financing could remain a stumbling block to that target, an already challenging goal given the large amounts of future doses secured with advance deals by major economies such as the United States, the European Union and Britain.

“At the moment we are not even on track to meet the target of the 20 per cent of the population of all the countries involved in Covax because there just hasn’t been enough investment,” said Deborah Gleeson, a senior lecturer at La Trobe University in Australia who specialises in access to medicines.

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The programme is about US$200 million shy of its US$2 billion 2020 target in finance for poorer countries, according to an October 8 update from Gavi, with a further US$5 billion needed next year. That money would help pay for doses for the 92 lower income countries included in Covax, while wealthier nations pay themselves for their doses procured through Covax.

The self-financing countries are a range of economies, including wealthy countries such as Britain and Japan and middle income economies like Thailand and Gabon.

Whether lower and middle income countries will get the same access to doses as the richer nations is a key consideration for these nations, said Swee Kheng Khor, a Malaysian doctor and global public health specialist.

“They will soon be asking questions about their priority in the pecking order of Covax,” he said.

Meanwhile, Gavi has offered the self-financing countries a so-called optional purchase arrangement that may make the flow of funds into the Covax facility less predictable.

Countries that choose this plan put down a larger upfront payment than those committing to Covid-19 vaccine purchases. But those countries can decide not to make full payment for a specific vaccine that becomes available if they opt for another later on.

Money from these self-financing countries allows Gavi to cut deals with vaccine makers to secure doses to ensure the 2 billion goal. Gavi aims to make as many as 15 agreements with vaccine makers by the end of 2020.

However, more countries were choosing the optional arrangement than anticipated, Gavi said at the end of September. That adds uncertainty to when money will be forthcoming, according to Yvette Madrid, a Switzerland-based global health consultant who has advised the WHO on immunisation campaigns.

“It adds risk … in terms of managing the flow of resources to ensure that there’s always enough money to keep this afloat to do what it needs to do at any given point in time,” Madrid said.

“[Gavi] really pushed the envelope, they’ve been super aggressive about doing this and they’ve had great success getting countries that people were not sure they were able to get,” she said.

“On the other hand, they still have financing questions and there’s this issue – is it going to be enough doses to really make a difference globally?”