Johnson & Johnson said Wednesday it was entering the final Phase 3 stage of its Covid-19 vaccine clinical trial following positive results in earlier stages.

The trial will seek to enroll up to 60,000 volunteers across more than 200 sites in the US and around the world, the company and the US National Institutes for Health (NIH), which is providing funding, said.

With the move, J&J becomes the tenth maker globally to conduct a Phase 3 trial against Covid-19, and the fourth in the US.

The company, which is developing the vaccine on a not-for-profit basis through its subsidiary Janssen, said it anticipated the drug would be ready for emergency approval by early 2021 if proven safe and effective.

"As COVID-19 continues to impact the daily lives of people around the world, our goal remains the same -- leveraging the global reach and scientific innovation of our company to help bring an end to this pandemic," said Alex Gorsky, the company's chairman and CEO.

Anthony Fauci, director of the NIH's National Institute of Allergy and Infectious Diseases, added: "Four COVID-19 vaccine candidates are in Phase 3 clinical testing in the United States just over eight months after SARS-CoV-2 was identified." 

"This is an unprecedented feat for the scientific community made possible by decades of progress in vaccine technology and a coordinated, strategic approach across government, industry and academia."

The US has given J&J about $1.45 billion in funding under Operation Warp Speed.

The vaccine is based on a single dose of a cold-causing adenovirus, modified so that it can no longer replicate, combined with a part of the new coronavirus called the spike protein that it uses to invade human cells.

J&J used the same technology in its Ebola vaccine which received marketing approval from the European Commission in July.

The company said it was poised to imminently publish the results from an earlier stage of the trial on a medical preprint site.

Pre-clinical testing on rhesus macaque monkeys that were published in the journal Nature showed it provided complete or near-complete protection against virus infection in the lungs and nose.

Like several other Phase 3 trials that are underway, its primary objective is to test whether the vaccine can prevent symptomatic Covid-19.