The Duke Global Health Innovation Center in Durham, North Carolina said low-income countries might have to wait until 2023 or 2024 to gain access to a safe and effective coronavirus vaccine.

Of all the groups that have joined the race to develop a COVID-19 vaccine, AstraZeneca, Pfizer, and Moderna are the ones closest to widespread distribution. All three vaccine developers have reported promising phase III trial results in recent weeks and estimated that with their forces combined, they could make sufficient doses for more than one-third of the world’s population by the end of 2021.

AstraZeneca, Pfizer, and Moderna have a total production capacity of 5.3 billion doses for 2021. If six other leading vaccine candidates are included, the total number of doses for which disclosed deals are in place will rise to 7.4 billion, accounting half of the world’s population.

Experts said, however, that not all countries will have immediate access to the COVID-19 vaccine as doses will not be distributed equitably. “Now that we are seeing really good results, everyone is feeling more optimistic,” said Andrea Taylor of Duke Global Health Innovation.

“They are starting to make deals. But it’s quite a scary picture at the minute, because so many countries are missing,” she added.

So far, all the 27 members of the European Union and five other wealthy nations have already pre-ordered more than half of the total doses to be produced by 2021. These rich countries account for only 13 percent of the global population.

Canada is the leading country when it comes to vaccine deals per capita, with nearly nine doses per person. “Canada has done exactly what we would expect a high-income country to do, and they’ve done the right thing by their country,” said Duke.

Duke explained that as local manufacturing deals determine where the initial shipments of COVID-19 vaccines go, low and middle-income countries will be left with dwindling short-term supplies. Unlike wealthy countries, poor countries will have to rely on contributions from COVAX, a joint fund for equitable distribution of the vaccines.

Duke said, however, that while countries with excess supplies of coronavirus vaccine doses might donate their surplus to COVAX, that would still not help with equitable distribution because high-income countries would certainly ensure that their own vaccine needs are met before they pass on their excess doses.

Meanwhile, AstraZeneca pledged to supply vaccine on a non-profit basis to low and middle-income countries for the duration of COVID-19. Other vaccine developers have yet to make such a commitment.

A man gets the flu vaccine in Mexico City. A man receives a vaccination by injection for seasonal flu, Type A influenza subtypes H1N1 and N3H3, at a subway station in downtown Mexico City January 29, 2014 Reuters/Tomas Bravo