Nigeria's health minister said on Wednesday some Covid-19 doses donated by rich Western countries had a shelf life that left only weeks to administer the shots.

Osagie Ehanire said the health ministry had declined a request by some vaccine manufacturers to extend the shelf life of the doses by three months.

Two sources have told Reuters that up to one-million Covid-19 vaccines are estimated to have expired in Nigeria last month without being used, one of the biggest single losses of doses that shows the difficulty African nations have getting shots in arms.

In response, Ehanire said in a statement expired vaccines had been withdrawn and would be destroyed by the National Agency for Food and Drug Administration. He did not give a figure.

He said if vaccines with a short shelf life arrive back-to-back or in large numbers, logistical bottlenecks occasionally arise.

"Some manufacturers offered to extend the vaccine shelf life after the fact, by 3 months, a practice that, though accepted by experts, is declined by the Federal Ministry of Health, because it is not accommodated in our standards," he said.

The World Health Organization said in a joint statement on November 29 with Africa's disease control body (Africa CDC), the GAVI vaccine alliance and other health groups that Covid-19 vaccines donated to African countries should have a minimum of 10 weeks shelf life when they arrive in-country.

Ehanire did not say exactly how long the vaccines had when they arrived but that Nigeria had been left with "a very short time, some just weeks, to use them, after deduction of time to transport, clear, distribute and deliver to users."

He said the issue of donations of doses with expiring shelf lives to developing countries was a matter that was under international discussion.

"Developing countries like Nigeria accept them because they close our critical vaccine supply gaps and, being free, save us scarce foreign exchange procurement cost," he said.