JOHANNESBURG (AP) — South Africa will start vaccinating front-line health workers next week with a shot that is still in testing — an unorthodox strategy announced Wednesday after officials scrapped plans to use another vaccine that a small study suggests is only minimally effective against the variant dominant in the country.

Health Minister Zweli Mkhize said South Africa would switch to the Johnson & Johnson vaccine and not use Oxford-AstraZeneca's — which was previously heralded as one of the most promising for the developing world because it's cheaper and does not require freezer storage like some other leading vaccines.

But a small study, which has not yet been peer-reviewed, suggested it was poor at preventing mild to moderate disease caused by the variant first detected in South Africa. Experts have said it might still work well against more severe disease.

Those results threw South Africa's vaccination campaign into disarray just as it was about to start administering the AstraZeneca vaccine — the only one authorized for general use in the country.

Officials quickly turned their focus to the one-shot J&J vaccine — which has only been approved for use in studies in South Africa and, in fact, hasn't yet been authorized for general use in any country. The company has applied for emergency use permission from the U.S. Food and Drug Administration and South Africa's regulatory authority.

Mkhize, in a nationally broadcast address, assured the public that the J&J vaccine is safe, pointing to the fact that it has been tested in 44,000 people so far. It will now be used to launch a drive to inoculate the country's 1.25 million health workers, he said.

“The Johnson & Johnson vaccine has been proven effective against the 501Y.V2 variant and the necessary approval processes for use in South Africa are underway,” he said, using the official name for the variant that experts say is more contagious. That variant recently drove a devastating resurgence of the pandemic with nearly twice the cases, hospitalizations and deaths experienced in the initial surge of the disease in the country.

A study of the J&J vaccine in South Africa, part of international trials, showed it was 57% effective at preventing moderate to severe COVID-19 in a test conducted when the variant was dominant. It provides even better protection against severe disease, with 85% efficacy after 28 days.

South Africa will begin administering the first shots next week, said Mkhize. The first round aims to reach 100,000 health care workers — and is officially being classified as a study of the vaccine, according to Dr. Glenda Gray, president of the South African Medical Research Council, who led the Johnson & Johnson tests here.

The first doses will come from vaccine sent to the country for testing purposes, and more are expected in March, when a South African pharmaceutical company begins bottling the vaccine here, Mkhize told a parliamentary committee Wednesday.

In all, the country hopes to vaccinate an estimated 40 million people by the end of the year — or about two-thirds of its population. South Africa plans to use the Pfizer vaccine — though it's not yet authorized — and is also considering others, including Russia's Sputnik V, China's Sinopharm and the Moderna one, Mkhize said. Unlike the J&J shot, none of those vaccines has been clinically tested against the variant prevalent in South Africa, although Pfizer has tested blood samples of people exposed to the variant.

The change of course came just one week after South Africa received its first vaccines — 1 million AstraZeneca doses, produced by the Serum Institute of India. But after results of the preliminary study were announced Sunday, South African officials quickly halted the planned rollout.

South Africa's abrupt cancellation could deal a blow to plans to use the vaccine widely, especially in many poorer countries, since it is being produced in large quantities in India and which the international COVAX facility has purchased in large numbers for distribution around the world.

An added complication for South Africa is that its AstraZeneca doses arrived with an April 30 expiration date. South Africa is looking to swap them, Mkhize said.

South Africa by far has the largest number of COVID-19 cases on the African continent with nearly 1.5 million confirmed, including almost 47,000 deaths. After a resurgence that spiked in early January, cases and deaths are now declining, but medical experts are already warning that South Africa should prepare for another upsurge in May or June, the start of the Southern Hemisphere's winter.

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