South Africa announced the suspension of its COVID-19 vaccinations on Sunday after a study showed that AstraZeneca vaccine failed to prevent mild and moderate cases of the virus variant that has appeared in the country.

Africa’s hardest-hit nation was due to start its vaccination campaign in the coming days with a million doses of the vaccine developed by AstraZeneca and Oxford.

“It’s a temporary issue that we have to hold on AstraZeneca until we figure out these issues,” Health Minister Zweli Mkhize said.

The University of Witwatersrand, Johannesburg, which conducted the trial, said in a statement on Sunday that the AstraZeneca vaccine “provides minimal protection against mild-moderate COVID-19 infection” from the South African variant”.

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But in a full paper due to be published on Monday, AstraZeneca said that none of the 2,000 participants developed serious symptoms.

That could mean it will still have an effect on severe illness, although not yet enough data is available to make a definitive judgement.

Lagging behind in the global vaccination race, South Africa received its first delivery of a million doses on Monday.

An additional 500,000 doses are expected this month.

All are AstraZeneca vaccines produced by the Serum Institute of India and some 1.2 million health workers are to be first in line for the shots.

“In the next four weeks, we will have the J&J and Pfizer,” said Mkhize, referring to vaccines made by Johnson & Johnson and Pfizer/BioNTech.

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Discussions with other vaccine producers are also ongoing, particularly Moderna and the makers of the Russian Sputnik V vaccine.

Mkhize recently announced having reserved 20 million Pfizer/BioNTech doses.

The 1.5 million AstraZeneca vaccines obtained by South Africa, which will expire in April, will be kept until scientists give clear indications on their use, he said.

“The second generation of the vaccine to fight all variants will take longer to produce,” said Salim Abdool Karim, epidemiologist and co-chair of the scientific committee at the South African health ministry.

South Africa plans to vaccinate at least 67% of its population by the end of the year, or around 40 million people.

The country has recorded more than 1.5 million infections and over 46,000 deaths from the virus.