South Africa on Sunday suspended plans to inoculate its front-line health care workers with the Oxford-AstraZeneca vaccine after a clinical trial suggested that it isn't effective in preventing mild to moderate illness from the variant dominant in the country.

The country received its first one million doses of the AstraZeneca vaccine last week and was expected to begin giving jabs to health care workers in the middle of this month.

But preliminary data from a small study suggested that the AstraZeneca vaccine offers only “minimal protection against mild-moderate disease" caused by the variant in South Africa.

The study, which hasn't yet been peer-reviewed, involved 2,000 people, most of whom were young and healthy. The volunteers’ average age was 31.

Salim Abdool Karim, chairman of South Africa's COVID-19 advisory committee, said there wasn't enough data on how well the vaccine protects against severe disease caused by the variant.

"The AstraZeneca vaccine rollout needs to be put on temporary hold while we get the clinical efficacy information," he said.

He added that there would only be a wide-scale rollout of the jab if new data on could show "acceptable" hospitalization rates.

Other vaccines have shown reduced efficacy against the variant, but have provided good protection from serious disease and death.

Health minister Zweli Mkhize said discussions were being held to explore available alternatives.

"There are discussions going on on Sputnik, Sputnik V. There are discussions going on about Sinopharm, the department and the ministerial advising committee are dealing with that. There are discussions that are going on with Moderna. And we will also need to explore on Novavax, that one there had not been much of discussion. So the discussion on all of them remains open", said Mkhize.