Johnson & Johnson vaccine, developed with Beth Israel, is 66 percent effective globally

The company plans to seek emergency use authorization early next month for the first coronavirus vaccine that would require only a single shot.

In March, research assistant Noe Mercado prepared a test in Barouch Laboratory at Beth Israel Deaconess Medical Center's Center for Virology and Vaccine Research.Craig F. Walker/Globe Staff

Johnson & Johnson said on Friday it would seek emergency use approval early next month for its one-shot coronavirus vaccine after results from a late-stage study showed it provided strong protection against COVID-19.

If the Food and Drug Administration grants the request, which seems likely amid the slow and uneven rollout of vaccines from Pfizer-BioNTech and Moderna, Johnson & Johnson has promised to deliver 100 million doses in the United States by the end of June. Because the vaccine can be administered in one shot ― unlike the other vaccines, which require two ― that would mean full coverage for 100 million people.

The vaccine uses technology pioneered by the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston. In the clinical trial, which involved 43,783 volunteers across the world, a single shot prevented 66 percent of moderate and severe cases globally, and 72 percent in the United States.

Worldwide, the shot prevented 85 percent of severe cases and none of the vaccinated people needed hospitalization or died from COVID-19, according to results released Friday morning by Johnson & Johnson and the National Institutes of Health.

The 66 percent global effectiveness rate fell significantly short of the performances of the two-shot vaccines from Pfizer-BioNTech and Moderna. They prevented about 95 percent of coronavirus cases in large trials, a remarkable showing considering that they were the first to successfully use new technology called synthetic messenger RNA.

But Dr. Dan Barouch, who runs the virology center at Beth Israel and is one of the world’s leading vaccine developers, said the pandemic has evolved, with the emergence of more resistant variants, in particular a worrisome South African strain that was detected in the United States for the first time this week.

“It’s not the same pandemic as it was a few months ago,” he said in a telephone interview. “This is very strong efficacy data against a complex pandemic involving multiple resistant variants circulating globally.”

Based on the data, Johnson & Johnson plans to apply to the FDA for emergency use in early February. It would be the third vaccine to receive that authorization, behind the vaccines from New York-based Pfizer and Cambridge-based Moderna. The company said it expects to have doses ready to ship “immediately” afterward.

Dr. Anthony Fauci, the nation’s top infectious disease expert, acknowledged that public health officials will likely face a “messaging challenge” to persuade people to take a vaccine that prevented 66 percent of symptomatic cases compared with roughly 95 percent.

But, he said, “If you can prevent severe disease in a high percentage of individuals [as the Johnson & Johnson vaccine did], that will alleviate so much of the stress and human suffering and death.”

He and other officials also said the Pfizer and Moderna vaccines would likely get lower efficacy results now, given the emergence of a South African strain that appears to be more resistant to immunization.

Johnson & Johnson and federal officials provided a comparison that illustrated how challenging the South African variant is to tame. The J&J vaccine prevented only 57 percent of moderate and severe cases at trial sites in South Africa, compared with 72 percent of such cases at multiple US trial sites.

Vaccine experts also cautioned that a head-to-head comparison of the three vaccines is tricky, even setting aside the recent appearance of resistant coronavirus strains. Moderna’s late-stage trial, for example, included study sites only in the United States, while the Johnson & Johnson and Pfizer trials had sites in other countries.

The FDA said last summer that a vaccine that was safe and at least 50 percent effective would likely be cleared for use.

Despite its lower performance in preventing all COVID-19 cases, the Johnson & Johnson vaccine would have significant advantages over its Pfizer-BioNTech and Moderna rivals. It requires only one shot, which would simplify and speed the vaccine campaign. In addition, it is stable at refrigerated temperatures, unlike the other vaccines, which must be frozen at ultracold temperatures when shipped and stored before use.

The FDA cleared the Pfizer-BioNTech vaccine on Dec. 11 and the Moderna vaccine a week later. But their rollout has been frustratingly slow and cumbersome, and public health officials have hungered for another vaccine to bolster the supply.

As of Friday morning, the government had distributed 49.2 million doses of both vaccines but only 27.9 million shots have been administered, according to the Centers for Disease Control and Prevention. President Biden, under intense pressure to accelerate the rollout, has vowed to take steps to ensure that 300 million Americans are vaccinated by the end of the summer.

His administration said Tuesday it was seeking to buy an additional 100 million doses each of the Pfizer and Moderna vaccines. That would increase available supply by 50 percent, bringing the total to 600 million doses by the summer.

Given the supply shortage, Dr. Paul Offit, a pediatrician specializing in infectious diseases at Children’s Hospital of Philadelphia, called the results of Johnson & Johnson’s trial “incredibly encouraging.”

“If you could walk into any grocery store anywhere and get an mRNA vaccine at your whim, that would be great, but we don’t live in that world right now,” said Offit, who sits on an advisory panel of outside experts that recommended the FDA clear the first two vaccines and is expected to consider Johnson & Johnson’s request. “The goal of this vaccine is to keep you out of the hospital and to keep you from dying.”

If the vaccine is cleared for emergency use, it might be deployed in regions of the country where local officials say residents are unlikely to adhere to a two-shot regimen or where clinics are struggling to satisfy the frigid storage requirements of the first two vaccines.

The Johnson & Johnson vaccine is one of six experimental vaccines that received billions of dollars in funding through the federal Operation Warp Speed program. That government effort picked up much of the development and manufacturing costs in the hopes of speeding regulatory approval and deployment.

The government will pay Johnson & Johnson more than $1 billion for 100 million doses and has an option to buy 200 million additional doses. The company has set a goal of providing 1 billion doses worldwide this year and will do so on a nonprofit basis during the pandemic.

The Johnson & Johnson vaccine relies on a design that Barouch pioneered nearly 20 years ago for two experimental vaccines that have shown promise against HIV and Zika, and a third vaccine that won approval from the European Union in July to prevent Ebola.

It uses a harmless and relatively rare cold virus, adenovirus serotype 26 ― or Ad26 ― as a Trojan horse to deliver part of the distinctive spike protein on the coronavirus surface into cells to trigger an immune response without making people sick.

After Barouch’s researchers tested it on animals in the spring, Johnson & Johnson launched an early-stage trial on about 1,000 volunteers during the summer. Updated results published this month in the New England Journal of Medicine showed that the vaccine generated antibodies in the blood after one shot, but that two doses produced more. Johnson & Johnson is running a second late-stage trial involving 30,000 volunteers to test the two-shot regimen.

Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine and an authority on vaccines, said he found the results “really promising.” He added that he suspects that two shots of the Johnson & Johnson vaccine would provide “durable protection at least as good” as the two-shot vaccines from Pfizer and Moderna.

“I hope we can scale production and get this to the American people soon,” he said in an e-mail.