Johnson & Johnson said on Friday that its single-dose vaccine was 66% effective in preventing COVID-19 in a large trial against multiple variants across three continents.
In the trial of nearly 44,000 volunteers, the level of protection against moderate and severe COVID-19 varied from 72% in the United States, to 66% in Latin America and just 57% in South Africa, from where a worrying variant has spread.
A high bar has been set by two authorized vaccines from Pfizer/BioNTech and Moderna, which were around 95% effective in preventing symptomatic illness in pivotal trials when given in two doses.
Those trials, however, were conducted mainly in the United States and before new variants emerged.
J&J's main goal was the prevention of moderate to severe COVID-19, and the vaccine was 85% effective in stopping severe disease and preventing hospitalization across all geographies and against multiple variants 28 days after immunization.
That "will potentially protect hundreds of millions of people from serious and fatal outcomes of COVID-19," Paul Stoffels, J&J's chief scientific officer, said in a statement with the results, which were based on 468 symptomatic cases.
J&J plans to seek emergency use authorization from the US Food and Drug Administration next week.
Public health officials have been counting on the J&J vaccine to increase much-needed supply and simplify the US immunization campaign.
"Right now, any protection and additional vaccine is great. The "South Africa" strain is still uncommon in the US and obviously we would want to see higher efficacy, but the key is not only overall efficacy but specifically efficacy against severe disease, hospitalization, and death," Walid Gellad, a health policy associate professor at the University of Pittsburgh said of the results.
None of the vaccine recipients in the J&J trial died from COVID-19, compared with 5 deaths in the placebo group, according to the National Institutes of Health, which said there were three deaths in the vaccine group overall, but none were determined to be from the virus.
That compares with 16 deaths overall in the placebo arm.
Unlike the Pfizer/BioNTech and Moderna vaccines, J&J's does not require a second shot weeks after the first or need to be kept frozen, making it a strong candidate for use in parts of the world with weak transportation infrastructure and insufficient cold storage facilities.
Several studies have emerged this month showing that a South African variant of the coronavirus has mutated in areas of the virus that are key targets of vaccines, reducing their efficacy.
"What we are learning is there is different efficacy in different parts of the world," Stoffels said in a telephone interview.
Importantly, though, in a sub-study of 6,000 volunteers in South Africa, Stoffels said, the J&J vaccine was 89% effective at preventing severe disease. Ninety-five percent of cases in the South Africa portion of the trial were infections with the South African variant.
A mid-stage trial of a Novovax Inc coronavirus vaccine in South Africa also showed lower efficacy in the country. It proved to be 60% effective among volunteers who didn't have HIV. In a separate, late-stage trial in the UK, the vaccine was 89.3% effective.
In the J&J trial, which was conducted in eight countries, 44% of participants were from the United States, 41% were from Central and South America and 15% were from South Africa. Slightly more than a third of the volunteers were over age 60.
J&J's vaccine uses a common cold virus known as adenovirus type 26 to introduce coronavirus proteins into cells in the body and trigger an immune response.
The Pfizer/BioNTech and Moderna vaccines use a new technology called messenger RNA (mRNA) that requires it to be stored in a freezer.
The news of another safe and effective vaccine comes as the United States has surpassed 430,000 COVID-19 deaths and with hospitals in many states still struggling to keep up with patients despite recent declines in new infections.
Concerns about fresh surges in the United States have also grown due to the presence of a more contagious coronavirus variant first discovered in the UK and news of the arrival of the South African variant on Thursday in South Carolina.
The US vaccination program got off to a slow start in December and has accelerated to around 1 million shots per day nationwide.
US President Joe Biden has promised that at least 100 million shots will be administered in his first 100 days in office, but concerns about supply disruptions have added uncertainty to that target.
The United States has an agreement to buy 100 million doses of J&J's vaccine for $1 billion. The company said in a statement the vaccine would be ready immediately upon emergency approval but Stoffels declined to specify how many doses. The government also has the option of purchasing an additional 200 million doses.
J&J has said it plans to deliver 1 billion doses in 2021 and will produce the vaccine in the United States, Europe, South Africa and India.