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

South Africa got its first 1 million doses of the AstraZeneca vaccine last week and was expected to begin giving shots to health care workers in mid-February. The disappointing early results indicate that an inoculation drive using the AstraZeneca vaccine may not be useful.

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 variant appears to be more infectious, and it is driving a deadly resurgence of the disease in the country, accounting for more than 90 percent of the Covid-19 cases, Health Minister Zweli Mkhize said Sunday night.

“The AstraZeneca vaccine appeared effective against the original strain but not against the variant,” Mkhize said. “We have decided to put a temporary hold on the rollout of the vaccine. … More work needs to be done.”

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.

“Protection against moderate-severe disease, hospitalization or death could not be assessed in this study as the target population were at such low risk,” said a statement issued by Oxford University and the University of the Witwatersrand in Johannesburg.

A vial of the Oxford-AstraZeneca Covid-19 vaccine.Peter Cziborra / ReutersScientists will study whether the AstraZeneca vaccine works against the variant to prevent death and severe disease, Mkhize said. Other vaccines have been less effective against the variant, but they have provided good protection against death and serious disease.

Public health officials are concerned about the South African variant because it includes a mutation of the coronavirus’s characteristic spike protein, which is targeted by existing vaccines. South African officials say the variant is more contagious, and evidence is emerging that it may be more virulent.

South Africa will urgently roll out other vaccines to inoculate as many people as possible in the coming months, Mkhize said. Other South African scientists said Sunday that clinical trials for the Johnson & Johnson vaccine show good results against the variant.

The early results for the AstraZeneca vaccine against the variant could have far-reaching implications, as many other countries in Africa and beyond have been planning to use the AstraZeneca shot. The international COVAX initiative has bought the AstraZeneca vaccine in bulk from the Serum Institute of India.

Developers of the Oxford-AstraZeneca vaccine expect to have a modified shot to cope with the South African coronavirus variant by autumn, the vaccine’s lead researcher, Sarah Gilbert, told the BBC on Sunday.

Authorities in England last week went house to house to test for Covid-19 in eight areas where the South African variant is believed to be spreading after a handful of cases were found in people who had had no contact with the country or anyone who had traveled there.

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.

Britain has had Europe’s deadliest coronavirus outbreak, with over 112,000 confirmed deaths, and it has embarked on a speedier vaccination plan than the neighboring European Union. So far, the U.K. has given first vaccine shots to about 11.5 million people.