When a plane loaded with 1 million doses of vaccine produced by AstraZeneca landed in South Africa on Feb. 1, a hopeful country watched with rapt attention.

Exactly a week later came the blow: A study, however limited and not yet peer-reviewed, said the vaccine provided only “minimal protection” against contracting mild to moderate infections of a new coronavirus variant that is widespread in South Africa, where it was first detected. The variant has since been found in at least 30 countries.

The news was a blow not only to South Africans but to billions of people whose governments are relying on the vaccine developed at Oxford University and made by AstraZeneca. If further studies confirm the finding about the effectiveness of the vaccine, dozens of countries around the world may need to adjust their vaccine rollout plans. South Africa, however, has the unwelcome role of going first.

For now, its government has suspended the use of the AstraZeneca vaccine and is trying to expedite its procurement of Johnson & Johnson, Pfizer and Moderna vaccines — though only the efficacy of the Johnson & Johnson vaccine has been studied in South Africa during the new variant’s predominance. In a much larger study than the AstraZeneca vaccine study, it was also found to be less effective against the variant but able to prevent severe cases and death almost totally. South Africa expects its first delivery in mid-February and hopes to use it to vaccinate a first phase of health workers, but it is still negotiating the size of the first batch.

South Africa has also ordered 20 million doses of the Pfizer vaccine, the country’s health minister told the Sunday Times newspaper on Jan. 29, but delivery dates had not been set.

“It’s a preview of what other places in the world will see. We are learning that vaccine rollouts will require continuous recalibration,” said Shabir Madhi, a professor of vaccinology at South Africa’s University of the Witwatersrand and chief investigator in the trial. “It can’t be a generic approach.”

The suspension announced by the South African government Sunday night was partly explained as a timesaving measure while researchers get better data about the AstraZeneca vaccine — particularly on how effective it is at preventing severe cases. The study, produced by researchers from the universities of Witwatersrand and Oxford, involved only 2,000 participants, half of whom got the vaccine while the other half got a placebo, and its median age was 31, meaning little could be gleaned about the vaccine’s efficacy against severe cases of the new variant or about how well it protects the elderly, who are the most likely to be hospitalized or die.

People should not conclude “that this vaccine doesn’t work at all,” Soumya Swaminathan, the World Health Organization’s chief scientist, said of AstraZeneca’s vaccine at a news conference Monday. “What we’ve seen is data from a small study. It’s indicative. It is telling us we need to collect more data, we need to study it more.”

At the same briefing, Seth Berkley, a top official administering the WHO-led effort to ensure vaccine supply to low-income countries, said the new research would not stop it from distributing more than 300 million doses of the AstraZeneca vaccine in a first round of deliveries beginning later this month.

On Sunday, however, South Africa’s health minister, Zweli Mkhize, said that more recalibration of the country’s response would be inevitable.

“Our scientists must get together and quickly figure out what approach we’re going to use,” he said. A spokesman for President Cyril Ramaphosa did not respond to requests for comment.

The new variant, known as B.1.351, drove a monster second wave in South Africa that subsided only after another round of lockdowns and other restrictions. More than 90 percent of new cases since December have been of the new variant, and studies showed tens of thousands of excess deaths during that period that experts said were largely attributable to it.

Thousands of variants are in circulation, but only a few such as B.1.351 have been treated as “variants of concern” because they are more transmissible, more lethal or are suspected of being able to dodge the antibodies produced by vaccination. Two others, first detected in Britain and Brazil, have also risen to that level and spread to dozens of countries.

Madhi said the proliferation of such variants would almost certainly continue, underscoring the need to spread vaccine studies around the world to better understand how they stand up to different variants.

“Without a study in South Africa, the entire world would’ve been oblivious to this,” he said. “I think what we’re now going to experience globally, especially in places with slow rollout, or with a huge amount of virus circulating like in the United States, is how continued mutations make new variants less susceptible to vaccines.”

Vaccine developers say they are creating “libraries” of tweaked vaccines that they could quickly test against emerging variants. They say new and improved versions of their vaccines could be tested and released within the year, if necessary.

Sarah Gilbert, one of the lead developers of the Oxford-AstraZeneca vaccine, said her laboratory and others are already working on ways to adjust their existing vaccines to meet the challenge of new variants.

“This year we expect to show that the new generation of the vaccine is able to generate antibodies that recognize the new variant,” she told the BBC. “And then it will be very much like working on flu vaccines. People will be familiar with the idea that we have to have new components in the flu vaccine every year to keep up with the main flu strains that are circulating, and there are regulatory procedures that were established for that.”

Britain is also relying heavily on the AstraZeneca vaccine and doesn’t expect doses of the Moderna vaccine until spring. Speaking to reporters Monday at a manufacturing facility for coronavirus tests, Prime Minister Boris Johnson said he was still “very confident” in the vaccine. British health regulators have approved vaccines by Pfizer, Moderna and AstraZeneca, which all show efficacy against the variant that was first identified in the U.K.

“I think it's important for people to bear in mind that all of them, we think, are effective in delivering a high degree of protection against serious illness and death, which is the most important thing. We also think, in particular in the case of the Oxford-AstraZeneca vaccine, that there’s good evidence it’s stopping transmission as well,” he said, citing preliminary and still-unconfirmed data.

Researchers in South Africa cautioned, however, that while data from the AstraZeneca trial in South Africa was limited, especially on the vaccine’s ability to prevent severe cases, the emergence of new, more concerning variants was almost assured.

“I would not be surprised if in a few weeks a relatively large percentage of the variant from Britain show nastier mutations similar to B.1.351 that result in reduced efficacy of vaccines,” said Tulio de Oliveira, the director of the KwaZulu-Natal Research Innovation and Sequencing Platform, or KRISP, a scientific organization that has played a key role in identifying and studying new variants.

DNA sequencing by KRISP has found that B.1.351 is probably already dominant in many countries bordering or close to South Africa, including Mozambique, Botswana and Zambia.

As South Africa scrambles to come up with a new inoculation plan, officials have begun to warn of a potentially severe third wave as soon as June, when the country heads into winter. At the news briefing Sunday, they stressed that sustained research was the only way to know how to respond.

“Science has to dictate what we do,” said Barry Schoub, chairman of the Ministerial Advisory Committee on coronavirus vaccines. “If we want to get the most effective bang for our buck, then we’ve got to use scientific information.”

Bearak reported from Nairobi, Booth from London and Wroughton from Cape Town.