The Serum Institute of India's (SII) inability to supply the vaccine following the banning of exports, means the Covax scheme is 140 million doses short.
Unicef, which purchases and distributes vaccines for Covax, is urging the G7 and EU nations to begin sharing doses with other parts of the world.
Unicef has estimated that the world’s richest countries can afford to donate more than 150 million doses to the scheme.
"Sharing immediately available excess doses is a minimum, essential and emergency stop-gap measure, and it is needed right now,” Unicef Executive Director Henrietta Fore said.
The G7 are set to meet in the UK next month, by which point Covax could be 190 million doses short of what it planned to be.
The SII planned to supply around half of the two billion vaccines required by Covax but has been unable to meet their obligations in March, April or May.
Boris Johnson has previously proposed to donate the majority of the UK’s vaccine supply to poor countries but he has offered no specific details on how or when this will be done.
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According to Unicef, the world’s richest countries could make up the shortfall without impacting their own supply.
For example, Canada has bought 338 million doses, which is sufficient to vaccinate the country’s population five times over.
The UK’s orders would allow them to fully vaccinate everyone three and a half times, indicating there is plenty of surplus.
African countries are the most reliant on Covax to supply their vaccine doses, leaving them vulnerable by the shortfall.
France, Belgium and Spain are among those to announce they will donate doses but Covax needs hundreds of millions more to meet demands.
It is feared if countries do not act to help, the consequences could be disastrous across the world.