South Africa is suspending its rollout of the Oxford/AstraZeneca coronavirus vaccine after findings suggested it offers limited protection against mild disease caused by the COVID-19 variant discovered there.
It follows disappointing results in a trial conducted by the University of the Witwatersrand, Health Minister Zweli Mkhize said.
The government had been intending to give the AstraZeneca jab to healthcare workers, after receiving a million doses produced by the Serum Institute of India last week.
Instead, it will offer those workers alternative vaccines from Pfizer and Johnson & Johnson (J&J) in the coming weeks.
In the meantime, scientists will consider how the AstraZeneca (AZ) shot can be deployed.
"What does (this) mean for our vaccination programme which we said will start in February? The answer is it will proceed," Mr Mkhize said in an online briefing.
"From next week, (and) for the next four weeks, we expect that there will be J&J vaccines, there will be Pfizer vaccines. So what will be available to the health workers will be those vaccines."
He added: "The AstraZeneca vaccine will remain with us, up until the scientists give us clear indications as to what we need to do."
Mr Mkhize said the variant is currently accounting for more than 90% of coronavirus
cases in South Africa.
A testing blitz in England is aiming to find "every single case"
of the mutation, after examples were found which appeared to have no links to international travel.
Scientists behind the Oxford/AstraZeneca jab hope to have a modified version ready by the autumn that will cope with the South Africa variant.
Professor Sarah Gilbert told the BBC: "We have a version with the South African spike sequence in the works."
Professor Shabir Madhi, who led trials of the AZ vaccine in South Africa, told Sky News it was likely the jab would still be used there, stressing that the findings are for mild infection only.
Noting that the technologies used to develop the AZ and J&J jabs are similar, he said: "The J&J vaccine in South Africa against the variant has been shown to reduce moderate to severe disease by 57%, and severe disease by as much as 89%.
"So I think there might still well be a role for the AZ vaccine, at least in terms of protecting against severe disease."
Prof Mahdi added that vaccines have a "huge role to play in terms of having an immediate impact" in saving people's lives.
He also urged rich countries, which may have ordered more doses than they need, to distribute them to poorer countries "immediately".
He said COVID-19
is a "global emergency" and the longer people have to wait to be inoculated, the more chance there is that new, "more resistant" variants will develop.
Earlier, a spokesman for AstraZeneca said
: "Early data has shown limited efficacy against mild disease primarily due to the B.1.351 South African variant.
"We do believe our vaccine could protect against severe disease, as neutralising antibody activity is equivalent to that of other COVID-19 vaccines that have demonstrated activity against more severe disease, particularly when the dosing interval is optimised to 8-12 weeks."
Reacting to the research in South Africa, which has not yet been peer reviewed, Peter Openshaw, professor of experimental medicine at Imperial College London, said the trial "seems to have been restricted to HIV negative younger people (mean age 31), (with) about 1,000 in the placebo arm and 1,000 in the active vaccine group".
He added that "vaccines that are effective against the more severe forms of disease may not affect milder forms".
There is "optimism that severe disease will still be prevented by vaccines", Prof Openshaw said.
Professor Anthony Harnden, deputy chair of the UK's Joint Committee on Vaccination and Immunisation, said: "Evidence suggests the Oxford AZ vaccine protects against disease caused by the predominant COVID variants circulating in the UK.
"It remains highly likely that the vaccine will also protect against severe disease caused by the South African variant."