Poor countries refused to take around 100 million donated Covid-19 vaccine doses in December alone, chiefly due to their short shelf life, the United Nations said Thursday.

The World Health Organization (WHO) has slammed the deadly "moral shame" of high-income countries hogging vaccine supplies then offloading near-expiry doses to jab-starved poorer nations.

Stark images last month of Nigeria disposing of more than a million AstraZeneca doses that had gone off highlighted the issue.

UNICEF, the UN Children's Fund, uses its vaccine logistics expertise to handle delivery flights for Covax, the global scheme set up to ensure a flow of doses to poorer nations.

In December, "we had almost more than 100 million doses that have been refused because of countries' capacities", UNICEF's supply division director Etleva Kadilli told a European Parliament committee.

"The majority of refusals are due to product shelf life."

"The short shelf life is really creating a major bottleneck for countries to plan their vaccination campaigns," Kadilli explained.

"Until we have a better shelf life, this is going to be a pressure point for the countries, specifically when countries want to reach populations in hard-to-reach areas."

European Union donations account for a third of the doses delivered so far via Covax, Kadilli told lawmakers.

Expired AstraZeneca vaccine doses at a dump in Abuja, Nigeria last month
Expired AstraZeneca vaccine doses at a dump in Abuja, Nigeria last month AFP / Kola Sulaimon

In October-November, 15 million EU-donated doses were rejected -- 75 percent of them AstraZeneca shots with a shelf life of less than 10 weeks upon arrival.

Kadilli said that several nations were requesting for deliveries to be put off until after March, when they might be better able to handle the pressure on the cold storage chain.

Many countries "come back and request split shipments -- they want to push doses towards the next quarter", she said.

"And I'm talking here also for large, big countries where naturally you'd think that they do have the capacity."

Covax is co-led by the WHO, the Gavi vaccine alliance, and CEPI, the Coalition for Epidemic Preparedness Innovations. Via UNICEF, it is about to deliver its billionth vaccine dose.

Worldwide, more than eight billion doses of Covid-19 vaccines have been administered so far in at least 219 territories, according to an AFP count.

Some 149 doses per 100 people have been injected in high-income countries -- and fewer than nine per 100 in the lowest-income nations.

On December 29, the WHO announced that 92 of its 194 member states had missed its target of vaccinating 40 percent of their population by the end of 2021.

"This is due to a combination of limited supply going to low-income countries for most of the year and then subsequent vaccines arriving close to expiry and without key parts like the syringes," said WHO chief Tedros Adhanom Ghebreyesus.

"It's not only a moral shame; it cost lives."