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A long-awaited single-dose coronavirus vaccine developed by Johnson & Johnson appears to be effective, company officials announced Friday, although it doesn’t offer as much protection as the two-dose vaccines currently on the market.

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Officials with Johnson & Johnson said the company’s vaccine proved to be 66% effective overall at preventing moderate to severe COVID-19 based on a late-stage trial that involved participants from the U.S. and seven other countries. It was more effective at preventing severe illnesses, at 85% effectiveness.

The results come from an ongoing trial involving about 44,000 volunteers from the U.S., Argentina, Brazil, Chile, Colombia, Mexico, Peru and South Africa.

Data announced Friday showed some geographic variation. In the U.S., the drug prevented moderate to severe COVID-19 infections in 72% of participants. In Latin America, the drug was 66% effective. It was 57% effective in South Africa, where a highly contagious new variant of the virus was recently discovered.

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With vaccinations off to a rocky start globally, experts had been counting on a one-dose vaccine that would stretch scarce supplies and avoid the logistics nightmare of getting people to return for boosters.

But with some other competing vaccines shown to be 95% effective after two doses, at question is whether somewhat less protection is an acceptable tradeoff to get more shots in arms quickly.

Experts told CNN that they expect the vaccine will still be useful at battling the ongoing pandemic.

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“The potential to significantly reduce the burden of severe disease, by providing an effective and well-tolerated vaccine with just one immunization, is a critical component of the global public health response,” Paul Stoffels, vice chairman of Johnson & Johnson’s executive committee and its chief scientific officer, said Friday in a news release.

“A one-shot vaccine is considered by the World Health Organization to be the best option in pandemic settings, enhancing access, distribution and compliance. Eighty-five percent efficacy in preventing severe COVID-19 disease and prevention of COVID-19-related medical interventions will potentially protect hundreds of millions of people from serious and fatal outcomes of COVID-19. It also offers the hope of helping ease the huge burden placed on healthcare systems and communities.”

Company officials said the vaccine is safe, and that the level of protection it provides was consistent across race and age groups. About a third of the study’s volunteers were over 60 years old and 41% had other existing health conditions, including obesity, type 2 diabetes, high blood pressure and HIV.

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Johnson & Johnson plans to file for emergency use authorization from the U.S. Food and Drug Administration within the next week. The company is the third to seek such authorization.

The FDA previously authorized emergency use of a vaccine developed by Pfizer and BioNTech and a separate vaccine developed by Moderna. Both vaccines require two doses and proved in clinical trials to be about 95% effective in preventing symptomatic illness. However, the trials were conducted before recently discovered, highly-contagious variants of the virus were found in the United Kingdom and South Africa.

As part of former President Donald Trump’s Operation Warp Speed, the federal government has invested about $1.5 billion into the development and manufacturing of the Johnson & Johnson vaccine, according to The New York Times. The agreement includes the delivery of 100 million doses of the company’s vaccine to the U.S. by the end of June, The Washington Post reported.

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The U.S. continues to lead the world in COVID-19 cases with 25.7 million reported nationwide as of Friday morning, according to a tally from Johns Hopkins University. More than 433,000 people have died of the viral infection in the U.S.

More than 101 million COVID-19 cases have been confirmed worldwide since the novel coronavirus first surfaced in China in late 2019. The virus has claimed 2.1 million lives globally.

The Associated Press contributed to this report.