Johnson & Johnson Reports Efficacy Rates of COVID-19 Vaccine Candidate


The single-dose adenovirus-based vaccine candidate produced protective effects against moderate-to-severe COVID-19, as well as against multiple virus variants.


Johnson & Johnson’s coronavirus disease 2019 (COVID-19) vaccine candidate is 66% effective in preventing moderate-to-severe COVID-19 and met all primary and secondary end points of its phase 3 ENSEMBLE clinical trial, according to a news release published on Friday.

The Janssen vaccine candidate has also been found to be effective against variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); currently, experts have identified COVID-19 variants in the United Kingdom, South Africa, and Brazil, all of which have been confirmed in the US.

Related: Emerging SARS-CoV-2 Variants, What You Need to Know

Unlike the Pfizer-BioNTech and Moderna vaccines currently being distributed to Americans, Johnson & Johnson’s COVID-19 vaccine candidate is a single-dose adenovirus-based vaccine that employs a portion of genetic material from a weakened pathogen in order to induce an immune response. The company leveraged its AdVac vaccine platform that has also been deployed to investigate Zika, RSV, and HIV investigational vaccine candidates.

The randomized, double-blind, placebo-controlled phase 3 ENSEMBLE study was conducted in 8 countries – the US, Argentina, Brazil, Chile, Colombia, Mexico, Peru, and South Africa – and included 43,783 participants who produced a total of 468 symptomatic cases of SARS-CoV-2.

The trial’s diverse population profile additionally revealed consistent protection against the virus across geographies and ages, including patients older than 60 years (n=13,610).

Researchers set co-primary end points of 14 and 28 days following vaccination and reported that the vaccine candidate was 85% effective in preventing severe disease across all study sites after 28 days. After day 49, investigators found no cases in vaccinated patients. “The Janssen COVID-19 vaccine candidate demonstrated complete protection against COVID-19 related hospitalization and death, 28-days post-vaccination,” according to the news release.

When taking into account emerging variants of the virus, the vaccine was 66% effective overall in preventing moderate-to-severe COVID-19 at 28 days post vaccination: 72% effective in the US, 66% effective in Latin America, and 57% effective in South Africa.

Investigators defined severe COVID-19 as laboratory-confirmed SARS-CoV-2 infection and at least 1 of the following:

  • Signs consistent with severe systemic illness
  • Admission to an intensive care unit
  • Respiratory failure
  • Shock
  • Organ failure
  • Death

Moderate COVID-19 disease was defined as confirmed infection, as well as evidence of pneumonia, deep vein thrombosis, shortness of breath or abnormal blood oxygen saturation above 93%, abnormal respiratory rate (≥20), or 2 or more of these symptoms.

The vaccine candidate’s safety profile is consistent with other vaccine candidates developed by Johnson & Johnson through its AdVac technology. Reported serious adverse events (SAEs) were higher in the placebo group and investigators did not observe any incidences of anaphylaxis.

“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 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.

“A 1-shot vaccine is considered by the World Health Organization to be the best option in pandemic settings, enhancing access, distribution, and compliance. 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. It also offers the hope of helping ease the huge burden placed on healthcare systems and communities,” he said.

Investigators aim to submit the results to a peer-reviewed journal in the next few weeks.


  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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