Johnson & Johnson becomes 4th manufacturer to begin Phase 3 trials for COVID vaccine

As the race for a safe and effective coronavirus vaccine continues, one manufacturer has announced a major step in the right direction.

American pharmaceutical company Johnson & Johnson said it will be starting Phase 3 clinical trials, joining Moderna, Pfizer and AstraZeneca to become the fourth manufacturer to initiate late stage testing in the United States, the last step before seeking authorization for distribution of a safe and effective vaccine.

Unlike its competitors, Johnson & Johnson's vaccine will be given as one shot rather than two different shots several weeks apart. If the vaccine is successful in late-stage trials, the more convenient dosing could make a big difference when it comes time for a nation-wide rollout. Logistics and supply will be an issue in any large scale distribution.

“A single dose is very important, we think, in a pandemic setting where, after 15 days, you're assumed to have protection,” Dr. Paul Stoffels, Johnson & Johnson’s chief scientist, told ABC News’ Bob Woodruff. “If you have a boosted dose with a one-month interval [in two-dose vaccines], it takes six weeks before you get protection.”

Stoffels also pointed out that an effective single-dose vaccine could in theory led to more availability and many more people being protected initially, compared to the Pfizer, Moderna and AstraZeneca vaccines that require two doses per person.

“If it works, yes, we can treat twice as many people," he said. "It's also a possibility to have faster impact on many more people.”

According to the National Institute of Allergy and Infectious Diseases, the trial will enroll over 60,000 participants in 215 locations across the U.S. and worldwide. This will make it the largest Phase 3 trial out of the four active vaccine candidates under the government's Operation Warp Speed.

Phase 3 clinical trials mark an important sign of progress and are generally the last phase before a product reaches the general public.

“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,” Dr. Anthony Fauci said in a statement.

“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,” he added.

Based on details from the trial, the Johnson & Johnson vaccine will be the first to require a single dose. Its storage requirements are also better-suited for an average doctor’s office or clinic, compared to Pfizer’s vaccine which needs deep-freeze storage.

“It is likely that multiple COVID-19 vaccine regimens will be required to meet the global need,” according to Fauci. “The Janssen [Johnson and Johnson’s parent company] candidate has showed promise in early-stage testing and may be especially useful in controlling the pandemic if shown to be protective after a single dose.”

With regards to the vaccine itself, it uses an “adenovirus vector” -- a modified copy of a common cold virus to induce immunity to COVID-19. This scientific technique has been previously employed in the Ebola vaccine, also by Johnson & Johnson, which gives the company an advantage, according to Stoffels.

It will take six weeks to two months to enroll the 60,000 participants needed in the final phase, with the goal to recruit a diverse study population, including patients with underlying conditions who may be at higher risk of complications from COVID-19, Stoffels said.

Stoffels told reporters on a conference call Tuesday that early-stage trial data will be released “imminently.”

Dave Harrison, M.D., is a pediatric cardiology fellow in Boston and a contributor to the ABC News Medical Unit.