Scientists will begin recruiting some 6,000 people across the U.K. on Monday for the 12-month trial.
Dr. Saul Faust, who is helping lead the study, said the research will start first in Britain but aims to recruit a total of 30,000 people in six countries around the world.
The shot uses a harmless cold virus to deliver the spike protein of the coronavirus into the body, which scientists hope will prompt an immune response.
Faust said the news from Pfizer and its German partner BioNTech last week that their vaccine appears to be 90% effective according to preliminary data was a welcome boost for their research.
Faust said half of the people in the new U.K. study will be given a placebo vaccine of saline. He added that researchers are hoping to recruit people from groups disproportionately affected by COVID-19, including older people and those of ethnic minorities.
The Jannsen vaccine is among the six experimental coronavirus vaccines that Britain has ordered as part of a planned 350 million-dose stockpile.