Johnson & Johnson Single-Dose Vaccine Effective Against COVID-19, Less So Against South African Variant


The level of protection for the single-dose COVID-19 vaccine was 72% in the United States compared to 57% in South Africa at 28 days post-vaccination, suggesting lower efficacy against the emerging South African variant.

Although an interim analysis of phase 3 data has found that the Johnson & Johnson single-shot coronavirus disease 2019 (COVID-19) vaccine offers protection, the efficacy was significantly lower in South Africa, where most cases are driven by a highly contagious variant.1

According to a press release, the investigational vaccine met all primary and key secondary endpoints, with topline safety and efficacy data based on 43,783 participants who accrued 468 symptomatic cases of COVID-19. The phase 3 ENSEMBLE study is designed to evaluate the efficacy and safety of the Janssen vaccine candidate in protecting against moderate to severe COVID-19, with co-primary endpoints of 14 days and 28 days following vaccination.1

Among all participants from different geographies and including those infected with an emerging viral variant, the vaccine candidate was 66% effective overall in preventing moderate to severe COVID-19 at 28 days after vaccination. The onset of protection was observed as early as day 14.1 Notably, the level of protection was 72% in the United States, 66% in Latin America, and 57% in South Africa at 28 days post-vaccination, suggesting lower efficacy against the emerging variant in South Africa.1

The first US cases of the South African variant have been detected in South Carolina, according to the CDC. Although there is no evidence at present that the variant causes more severe disease, preliminary data suggest that it may spread more easily and quickly than other variants.2

“Our goal all along has been to create a simple, effective solution for the largest number of people possible, and to have maximum impact to help end the pandemic,” said Alex Gorsky, MBA, chairman of the Board of Directors and CEO of Johnson & Johnson, in a press release. “We’re proud to have reached this critical milestone and our commitment to address this global health crisis continues with urgency for everyone, everywhere.”1

The vaccine candidate was 85% effective in preventing severe disease across all regions studied at 28 days post-vaccination in adults 18 years of age and older. Efficacy increased over time with no vases in vaccinated participants reported after day 49, according to the press release.1

The candidate also demonstrated complete protection against COVID-19-related hospitalization and death at 28 days post-vaccination and there was a clear effect on cases requiring medical intervention. There were no reported cases of COVID-19 requiring hospitalization among participants who had received the Janssen COVID-19 vaccine candidate at 28 days post-vaccination.1

“These topline results with a single-shot COVID-19 vaccine candidate represent a promising moment,” said Paul Stoffels, MD, vice chairman of the executive committee and chief scientific officer at Johnson & Johnson, in a press release. “The potential to significantly reduce the burden of severe disease, by providing an effective and well-tolerated vaccine with just 1 immunization, is a critical component of the global public health response.”1

The safety profile was consistent with other vaccine candidates using Janssen’s AdVac technology among more than 200,000 people to date. Overall fever rates were 9% and grade 3 fever was fewer than 0.2%. Overall serious adverse events reported were higher among participants who received the placebo compared to the active vaccine candidate and no anaphylaxis was observed.1

The press release noted that the vaccine candidate is compatible with standard vaccine distribution channels and is estimated to remain stable for 2 years at negative 4 degrees Fahrenheit, at least 3 months of which can be at temperatures between 36 and 46 degrees Fahrenheit. If approved, the company said it will ship the vaccine using the same cold chain technologies it uses today to transport other medicines and vaccines.1

“Changing the trajectory of the pandemic will require mass vaccination to create herd immunity, and a single-dose regimen with fast onset of protection and ease of delivery and storage provides a potential solution to reaching as many people as possible,” said Mathai Mammen, MD, PhD, global head of Janssen research & development, in the press release. “The ability to avoid hospitalizations and deaths would change the game in combating the pandemic.”1


Johnson & Johnson Announces Single-Shot Janssen COVID-19 Vaccine Candidate Met Primary Endpoints in Interim Analysis of its Phase 3 ENSEMBLE Trial [news release]. Johnson & Johnson; January 29, 2021. Accessed January 29, 2021.

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