Experts say there are several reasons why COVID-19 vaccination rates are still low in some countries, in addition to limited supplies.
Other challenges now include unpredictable deliveries, weak health care systems and vaccine hesitancy.
Many countries with low vaccination rates are in Africa.
Other places include Yemen, Syria and Haiti.
For most of last year, developing nations were plagued by a lack of supplies.
Other setbacks have emerged including poor infrastructure to distribute the shots and a lack of materials like syringes.
Vaccine hesitancy has also contributed to low uptake.
