Johnson & Johnson Single-Shot Janssen COVID-19 Vaccine Candidate 66% Effective in Phase 3 Study

Johnson & Johnson (New Brunswick, NJ, USA) has announced topline efficacy and safety data from the Phase 3 ENSEMBLE clinical trial, demonstrating that the investigational single-dose COVID-19 vaccine in development at its Janssen Pharmaceutical Companies (Beerse, Belgium) met all primary and key secondary endpoints.

The Phase 3 ENSEMBLE study is designed to evaluate the efficacy and safety of the Janssen COVID-19 vaccine candidate in protecting moderate to severe COVID-19, with co-primary endpoints of 14 days and 28 days following vaccination. The topline safety and efficacy data are based on 43,783 participants accruing 468 symptomatic cases of COVID-19. Among all participants from different geographies and including those infected with an emerging viral variant, Janssen’s COVID-19 vaccine candidate was 66% effective overall in preventing moderate to severe COVID-19, 28 days after vaccination. The onset of protection was observed as early as day 14. The level of protection against moderate to severe COVID-19 infection was 72% in the US, 66% in Latin America and 57% in South Africa, 28 days post-vaccination.


The vaccine candidate was 85% effective in preventing severe disease across all regions studied, 28 days after vaccination in all adults 18 years and older. Efficacy against severe disease increased over time with no cases in vaccinated participants reported after day 49. The Janssen COVID-19 vaccine candidate demonstrated complete protection against COVID-related hospitalization and death, 28 days post-vaccination. There was a clear effect of the vaccine on COVID-19 cases requiring medical intervention (hospitalization, ICU admission, mechanical ventilation, extracorporeal membrane oxygenation (ECMO), with no reported cases among participants who had received the Janssen COVID-19 vaccine, 28 days post-vaccination.

“These topline results with a single-shot COVID-19 vaccine candidate represent a promising moment. The potential to significantly reduce the burden of severe disease, by providing an effective and well-tolerated vaccine with just one immunization, is a critical component of the global public health response,” said Paul Stoffels, M.D., Vice Chairman of the Executive Committee and Chief Scientific Officer, Johnson & Johnson. “A one-shot vaccine is considered by the World Health Organization to be the best option in pandemic settings, enhancing access, distribution and compliance. 85% efficacy in preventing severe COVID-19 disease and prevention of COVID-19-related medical interventions will potentially protect hundreds of millions of people from serious and fatal outcomes of COVID-19. It also offers the hope of helping ease the huge burden placed on healthcare systems and communities.”

“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. The ability to avoid hospitalizations and deaths would change the game in combating the pandemic,” said Mathai Mammen, M.D., Ph.D., Global Head, Janssen Research & Development.

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