Johnson & Johnson single-shot vaccine 85% effective against severe COVID-19 disease

In another promising development for vaccine science, Johnson & Johnson says its vaccine -- a single shot tested against a complex barrage of newly emerged COVID-19 variants -- is 66% effective at preventing symptomatic disease and 85% effective against preventing severe illness.

A team of scientists at the company were "elated" and "joyful" when they saw the results, Dr. Mathai Mammen, M.D., Ph.D., the global head of Janssen Research & Development, told ABC News.

"We're a single shot ... And now we've produced data that say that our vaccine is highly effective, 85% effective against severe COVID, 100% effective against hospitalization or death," Mammen said.

"We've had the objective of producing a vaccine for the world, that is easily used, is easily distributed and it works against preventing the form of COVID-19 that people care about," said Mammen, meaning an illness that can make you severely sick at home and lead to hospitalization or death.

In a press release, Johnson & Johnson said the vaccine is also safe to take. Volunteers experienced mild reactions after the shot, with less than 10% experiencing fever.

The full data package will be made publicly available and will be evaluated by the FDA's advisory committee sometime in mid- to late February.

The Food and Drug Administration (FDA) has said it will consider a vaccine that's more than 50% effective, and the Johnson & Johnson vaccine exceeds this threshold. An emergency use authorization could be given and people could start receiving shots before the end of February.

With its single-shot administration and more convenient transportation and storage requirements, Mammen calls it a "workhorse vaccine."

"We're delighted to see that this vaccine has good efficacy against mild disease [and] outstanding efficacy against severe disease ... [in] all geographic regions studied," said Dr. Dan Barouch of the Beth Israel Deaconess Medical Center, who collaborated with Johnson & Johnson in the development of the vaccine.

Although existing FDA-authorized vaccines from Pfizer/BioNTech and Moderna boast roughly 95% efficacy rates against symptomatic disease, and near-perfect protection against severe illness, they also have drawbacks, as they both must be administered in two shots and have more complex storage requirements.

Also, they were tested back in the summertime, prior to the emergence of the recently discovered COVID-19 variants.

"They did run the vaccine at a period that was simpler," said Mammen. "These variants are particularly tricky as they can be more virulent [and] a little bit harder to protect from."

The Johnson & Johnson trial, launched in September, was conducted in the United States, South Africa and Latin America. Although unforeseen at the time, this massive clinical experiment comprised of more than 44,000 volunteers took place in countries were new COVID-19 variants would emerge shortly thereafter, often taking over the prior versions of the virus.

South Africa in particular is home to a variant that seems not only more transmissible, but is also seemingly able to blunt the effect of other existing vaccines. Latin America, meanwhile, is home to a more transmissible Brazilian variant that shares some of the same mutations.

"It's a much more complex pandemic now than it was months ago," Barouch said.

Broken down by region, the Johnson & Johnson vaccine, in the trial, was 72% effective in the U.S., 66% in Latin America and 57% in South Africa.

Mamment said the company is "very fortunate" to have chosen South Africa as one of the homes for its trial, because it gave them the opportunity to show that their vaccine works even against a variant that may one day become dominant.

So now, Mamment said, "I'm thinking not so much about the South African strain, but rather about other mutations that might pop up."

He's particularly encouraged by the fact that all volunteers saw a significant benefit in taking a vaccine that eliminates the possibility of being hospitalized with or dying of COVID-19.

In the trial, the Johnson & Johnson vaccine proved to be roughly 66% effective at stopping a person from developing COVID-19 with symptoms. But it was 85% effective at preventing severe illness that could send a person to the hospital.

"So, this is probably the single most exciting result in our entire clinical study that we have 85% protection against severe COVID, irrespective of where in the world you're talking about and what kind of variants you're talking about," Mamment said.

"From the standpoint of making a vaccine for this pandemic, your goal is keeping people out of the hospital and out of the morgue," said Dr. Paul Offit, a member of the FDA's advisory committee, director of the Vaccine Education Center and professor of pediatrics in the Division of Infectious Diseases at Children's Hospital of Philadelphia.

"Obviously it's no fun having mild illness," Offit said. "But the real question is: How effective was it at keeping people out of the hospital?"

The development comes as the world has been waiting for a more convenient, single-dose vaccine against the coronavirus -- and preferably one that doesn't need to be frozen for shipping and long-term storage, like Pfizer's and Moderna's do.

Mamment said his company's vaccine checks those boxes.

"We know it's a magnificent advantage to have a single shot," he said. "I believe everybody benefits from this vaccine."

They are now planning studies in children and pregnant women to ensure the vaccine is also safe and effective for those groups.

If authorized, the Johnson & Johnson vaccine would help ease a strained vaccine supply.

The company said they can deliver 100 million doses to the U.S. by June, if the FDA gives the green light.