Poorer nations last month rejected more than 100 million doses of COVID-19 vaccines distributed by the global programme COVAX, mainly due to their rapid expiry date, according to UNICEF.
The figure shows the difficulties of vaccinating the world despite growing supplies of jabs, with COVAX getting closer to delivering 1 billion doses to a total of nearly 150 countries.
"More than 100 million have been rejected just in December alone," Etleva Kadilli, director of Supply Division at UN agency UNICEF told lawmakers at the European Parliament.
Poorer nations have also been forced to delay supplies because they have insufficient storage facilities, Ms Kadilli said, including a lack of fridges for vaccines.
UNICEF's data on supplies and use of delivered vaccines show that 681 million shipped doses are currently unused in about 90 poorer nations across the world, according to CARE, a charity, which extracted the figures from a public database.
More than 30 poorer nations, including big states such as the Democratic Republic of Congo and Nigeria, have so far used fewer than half of the doses they have received, CARE said, citing UNICEF data.