A large number of poorer countries receiving Covid-19 vaccines through a global sharing scheme do not have enough doses to continue programmes, the World Health Organization has said.
WHO senior adviser Dr Bruce Aylward said the Covax programme had delivered 90 million doses to 131 countries.
But he said this was nowhere near enough to protect populations from a virus still spreading worldwide.
The shortages come as some nations in Africa see a third wave of infections.
On Monday, South African President Cyril Ramaphosa called for an end to vaccine hoarding by wealthier countries as his government scrambled to curb a steep rise in cases.
On a continental level, only 40 million doses have been administered so far in Africa – less than 2% of the population, Mr Ramaphosa said.
Covax was created last year to ensure Covid-19 doses were made available around the world, with richer countries subsidising costs for poorer nations.
Led by the WHO and other international organisations, Covax initially set a target of providing two billion doses worldwide by the end of 2021.
Most of those are being donated to poorer countries, where Covax hopes to distribute enough vaccines to protect at least 20% of the populations.
However, the distribution of these vaccines has been hampered by manufacturing delays and supply disruptions, leading to shortages in countries wholly reliant on Covax.
Uganda, Zimbabwe, Bangladesh and Trinidad and Tobago are just some of the countries that have reported running out of vaccines in recent days.