Topline data from a phase 3 trial evaluating the single-dose vaccine candidate JNJ-78436725 (Ad.26.COV2.S; Janssen) against coronavirus disease 2019 (COVID-19) showed that it met all primary and key secondary end points.

JNJ-78436725 is a recombinant vector vaccine that utilizes the Company’s AdVac® technology. It works by using a human adenovirus to express the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. 

The randomized, double-blind, placebo-controlled ENSEMBLE trial included 44,325 adults in Argentina, Brazil, Chile, Colombia, Mexico, Peru, South Africa, and the United States (US). Participants were randomly assigned to receive JNJ-78436725 or placebo intramuscularly as a single dose. Outcome measures included prevention of molecularly confirmed moderate to severe COVID-19 disease at 14 days and 28 days post-vaccination.

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An interim analysis (based on 43,783 participants and 468 symptomatic cases) showed that the vaccine candidate was 66% effective in preventing moderate to severe COVID-19 at 28 days post-vaccination among all participants, including those infected with an emerging viral variant; onset of protection was observed as early as day 14. The level of protection against moderate to severe COVID-19 at 28 days post vaccination was 72% in the US, 66% in Latin American countries, and 57% in South Africa. Across all geographical regions, the vaccine candidate was found to be 85% effective in preventing severe/critical COVID-19.

Moreover, the vaccine candidate demonstrated complete protection against COVID-19 related hospitalization and death at 28 days post vaccination. There were no reported COVID-19-related deaths in the vaccine arm compared with 5 in the placebo arm.

Trial participants will be followed for up to 2 years to further assess efficacy and safety. The study is being conducted in collaboration with the Biomedical Advanced Research and Development Authority and the National Institute of Allergy and Infectious Diseases.

“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,” said Paul Stoffels, MD, Vice Chairman of the Executive Committee and Chief Scientific Officer, Johnson & Johnson. “Eighty-five percent 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.”

The Company intends to file for Emergency Use Authorization (EUA) in early February and expects to have the vaccine available to ship immediately if authorized. The vaccine is estimated to remain stable for 2 years at -20°C (-4°F) and at least for 3 months at 2-8°C (36°F–46°F).

Additionally, the phase 3 ENSEMBLE 2 study is currently investigating different doses and dosing regimens of the vaccine candidate for the prevention of moderate to severe/critical COVID-19.


  1. Johnson & Johnson announces single-shot Janssen COVID-19 vaccine candidate met primary endpoints in interim analysis of its phase 3 ENSEMBLE trial. [press release]. New Brunswick, NJ: Johnson & Johnson; January 29, 2021. 
  2. Janssen investigational COVID-19 vaccine: interim analysis of phase 3 clinical data released. [press release]. Bethesda, MD: National Institutes of Health; January 29, 2021.

This article originally appeared on MPR