MONDAY, Feb. 8, 2021 — Plans to vaccinate frontline health workers with the Oxford-AstraZeneca COVID-19 vaccine have been delayed by South Africa because there are questions about its effectiveness.

Preliminary data from a small clinical trial indicate that the vaccine provides only “minimal protection against mild-moderate disease” caused by a more infectious variant of the coronavirus that’s dominant in South Africa, the Associated Press reported.

The study — which included 2,000 people, average age 31 — hasn’t been peer-reviewed.

“The AstraZeneca vaccine appeared effective against the original strain, but not against the variant,” Zweli Mkhize, South Africa’s health minister, said Sunday night, the AP reported. “We have decided to put a temporary hold on the rollout of the vaccine … more work needs to be done.”

After receiving its first 1 million doses of the vaccine last week, South Africa had planned to start inoculating health care workers in mid-February, the AP reported.

The coronavirus variant that’s dominant in South Africa appears more infectious and currently accounts for more than 90% of the COVID-19 cases in the country, Mkhize said.

The study couldn’t assess the AstraZeneca vaccine’s effectiveness in preventing “moderate-severe disease, hospitalization or death” because “the target population were at such low risk,” according to a statement from Oxford University and the University of the Witwatersrand in Johannesburg.

That’s something researchers plan to examine, Mkhize said.

A modified version of the Oxford-AstraZeneca vaccine that’s effective against the South Africa coronavirus variant should be ready by autumn, the vaccine’s lead researcher said Sunday, the AP reported.

South Africa will now roll out other vaccines to inoculate as many as possible in the coming months, Mkhize said. Other South African scientists said Sunday said the clinical trials for the single-dose Johnson & Johnson vaccine have shown good results against the variant.

Meanwhile, health officials in England went house-to-house last week to administer COVID-19 testing in eight areas where the South Africa variant is believed to be spreading, after a handful of cases were found in people who had no contact with South Africa or anyone who traveled there, the AP reported.

More than 100 cases of the South African variant have been found in the U.K. The testing blitz is a bid to snuff out the variant before it spreads widely and undermines the U.K.’s vaccination rollout, the AP said.

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