The Serum Institute of India, the world's biggest vaccine maker, let Africa down by pulling out of talks to supply Covid-19 vaccines, creating distrust that has affected demand, the head of the Africa Centres for Disease Control said on Thursday.

John Nkengasong denounced recent comments from Serum that uptake of its Covid-19 shots had slowed because of low demand from Africa and vaccine hesitancy, saying the real problem was that Serum had acted unprofessionally.

Serum did not immediately respond to a Reuters request for comment.

Nkengasong said Serum had engaged in discussions last year with the Africa Vaccine Acquisition Task Team (AVATT), and that at one point he had believed a deal was very close, but then Serum abruptly ended the talks.

"Serum just decided to act in a very unprofessional manner and stop communicating with AVATT team, so that created a situation where we found ourselves extremely unhappy ... and then engaged with Johnson & Johnson," he said.

African countries had agreed to buy 400 million doses of Covid vaccines from J&J, abandoning efforts with Serum, he said.

Then, earlier in 2021, came India's decision to ban vaccine exports as domestic infections soared, which had created further distrust abroad, and that explained the lack of demand from Africa for Serum's vaccines, Nkengasong said.

"If now Serum is shipping vaccines to COVAX, I don't know the mechanics of what volumes they are shipping to COVAX, but it will not surprise me that countries are now looking at that (thinking) 'OK, we needed you and you were not there for us'," he said.

Global vaccine-sharing network COVAX is still seeing strong demand for Serum's AstraZeneca shot, one of its backers GAVI said on Thursday, following comments from Serum that uptake had slowed.

Nkengasong described as "condescending" comments by Adar Poonawalla, the chief executive of Serum, in a recent interview with British newspaper The Times about low demand from Africa.

"It’s a combination of vaccine hesitancy and nations not coming forward and placing orders in the way in which they claim they would, particularly the African nations," Poonawalla was quoted as saying. "I’m happy to say that on record and I hope they read it because maybe they’ll get activated and do something about it."

Although vaccine supplies have started increasing to Africa, where just 7.5% of its more than 1 billion people are fully vaccinated, many African nations are finding they do not have the capacity to manage the shots.

Up to a million unused vaccine doses supplied via COVAX are estimated to have expired in Nigeria last month, underscoring the difficulty African countries have getting shots in arms, Reuters reported this week.