This September 2020 photo from Johnson & Johnson shows a single-dose COVID-19 vaccine being developed by the company. Cheryl Gerber / Courtesy Johnson & Johnson / AP

Johnson & Johnson’s vaccine candidate Covid-19 will begin phase 3 trials in the United States on Wednesday. Trials of the single-dose vaccine, using a human adenovirus, will enroll up to 60,000 adult participants in nearly 215 locations in the United States and internationally.

The vaccine candidate was developed by Janssen Pharmaceutical Companies, a subsidiary of Johnson & Johnson. Phase 3 studies will begin immediately. The first participants will receive doses on Wednesday, said Dr. Paul Stoffels, Johnson & Johnson’s Chief Scientific Officer, on a call with reporters Tuesday.

Initial results from Phase 1/2 studies of the vaccine in the US and Belgium suggest that the vaccine elicits an immune response and is safe enough for large-scale studies to be conducted.

Phase 3 studies are testing the safety and effectiveness of a single dose versus a placebo to prevent symptomatic Covid-19. The fact that the study is looking at the effectiveness of a single dose of the vaccine instead of two doses should speed up results, Stoffels said.

The trials are being carried out in Argentina, Brazil, Chile, Colombia, Mexico, Peru, South Africa and the United States. Johnson & Johnson intends to work with the UK government to conduct a separate phase 3 study to evaluate the effectiveness of two doses

If the vaccine is shown to be safe and effective, Johnson & Johnson expects the first doses to be available from the U.S. Food and Drug Administration for approval for emergency use by early 2021.

Where are things: Moderna, Pfizer / BioNTech, and AstraZeneca also have Covid-19 vaccine candidates in Phase 3 trials in the US, although AstraZeneca’s trial is currently on hold.

Johnson & Johnson’s Phase 3 study is being conducted in partnership with Operation Warp Speed, the federal government’s coronavirus vaccine.

Dr. Gupta discusses Johnson & Johnson’s vaccine: