Johnson & Johnson said on Friday that its single-dose vaccine was 66% effective in preventing Covid-19 in a large global trial against multiple variants which will give health officials another weapon to tackle the coronavirus.

In the trial of nearly 44,000 volunteers, the level of protection against moderate and severe Covid-19 varied from 72% in the United States, to 66% in Latin America and just 57% in South Africa, from where a worrying variant has spread.

A high bar has been set by two authorized vaccines from Pfizer/BioNTech and Moderna, which were around 95% effective in preventing symptomatic illness in pivotal trials when given in two doses.

Those trials, however, were conducted mainly in the United States and before new variants emerged.

J&J’s main goal was the prevention of moderate to severe Covid-19, and the vaccine was 85% effective in stopping severe disease and preventing hospitalization across all geographies and against multiple variants 28 days after immunization.

That “will potentially protect hundreds of millions of people from serious and fatal outcomes of Covid-19,” Paul Stoffels, J&J’s chief scientific officer, said in a statement with the results, which were based on 468 symptomatic cases.

J&J plans to seek emergency use authorization from the US Food and Drug Administration next week. It has said it plans to deliver 1 billion doses in 2021 and will produce the vaccine in the United States, Europe, South Africa and India.

Public health officials have been counting on the J&J vaccine to increase much-needed supply and simplify the US immunization campaign.

The United States has a deal to buy 100 million doses of J&J’s vaccine and an option for an additional 200 million. J&J said the vaccine would be ready immediately upon emergency approval, but Stoffels declined to specify how many doses.

“Right now, any protection and additional vaccine is great,” Walid Gellad, a health policy associate professor at the University of Pittsburgh said.

“The “South Africa” strain is still uncommon in the US and obviously we would want to see higher efficacy, but the key is not only overall efficacy but specifically efficacy against severe disease, hospitalization, and death,” Gellad added.

None of the vaccine recipients in the J&J trial died from Covid-19, compared with 5 deaths in the placebo group, according to the National Institutes of Health.

The NIH said there were three deaths in the vaccine group overall, but none were determined to be from the virus. That compares with 16 deaths overall in the placebo arm.

Unlike the Pfizer and Moderna vaccines, J&J’s does not require a second shot weeks after the first or need to be kept frozen, making it a strong candidate for use in parts of the world with where transportation and cold storage are an issue.

South Africa

Several studies have emerged this month showing that a South African variant has mutated in areas of the virus that are key targets of vaccines, reducing their efficacy.

“What we are learning is there is different efficacy in different parts of the world,” Stoffels told Reuters.

In a sub-study of 6,000 volunteers in South Africa, Stoffels said, the J&J vaccine was 89% effective at preventing severe disease. In the South Africa portion of the trial, 95% of cases were infections with the South African variant.

“I am overwhelmed by the fact that this vaccine protected against severe disease even in South Africa,” said Glenda Gray, the joint lead investigator of the South African vaccine trial.

Gray, who is the chief executive of the South African Medical Research Council, said this is by far the best vaccine for South Africa to fight the mutant strain and can prevent a large number of hospitalisations and deaths.

A mid-stage trial of a Novovax coronavirus vaccine in South Africa also showed lower efficacy, proving to be 60% effective among volunteers who didn’t have HIV. In a separate, late-stage trial in Britain it was 89.3% effective.

In the J&J trial, which was conducted in eight countries, 44% of participants were from the United States, 41% from Central and South America and 15% from South Africa. Slightly more than a third of the volunteers were over 60.

J&J’s vaccine uses a common cold virus to introduce coronavirus proteins into cells in the body and trigger an immune response, whereas the Pfizer/BioNTech and Moderna vaccines use a new technology called messenger RNA (mRNA).

The news of another safe and effective vaccine comes as the United States has surpassed 430,000 Covid-19 deaths and with hospitals in many states struggling to keep up with patients despite recent declines in new infections.