A child receives anti-polio vaccination at a healthy center in Sanaa, Yemen, on Feb. 20, 2017. (Xinhua/Mohammed Mohammed)

UNITED NATIONS, April 26 (Xinhua) -- The UN Children's Fund (UNICEF) said Wednesday that it procured 2.5 billion doses of vaccines to children in nearly 100 countries in 2016, reaching almost half of the world's children under the age of five.

These figures, released during World Immunization Week, make UNICEF the largest buyer of vaccines for children in the world, said Stephane Dujarric, spokesperson for UN Secretary-General Antonio Guterres, at the daily news briefing.

Nigeria, Pakistan and Afghanistan, the three remaining polio-endemic countries, each received more doses of vaccines than any other country, said Dujarric.

"Access to immunization has led to a dramatic decrease in deaths of children under five from vaccine-preventable diseases, and has brought the world closer to eradicating polio," he said.

Yet an estimated 19.4 million children around the world still miss out on full vaccinations every year because of conflicts, weak health systems, poverty or social inequities, said the spokesman.