ENSEMBLE Trial: J&J COVID-19 Vaccine Phase 3 Interim Analysis

Johnson & Johnson released interim analysis of its phase 3 EMSEMBLE trial for Ad.26.COV2, and provided more insight on overall protection in various countries, variant protection, and clinical outcomes.

Johnson & Johnson’s (J&J) coronavirus disease 2019 (COVID-19) vaccine is 66% effective at preventing both moderate and severe COVID-19 at day 28 post-vaccination, according to phase 3 interim results published by the National Institutes of Health.1

J&J’s vaccine, Ad.26.COV2, is a single injection and can be stored in the refrigerator for months. It is indicated for adults aged 18 years and older.

The interim analysis (N=43,783) assessed 468 cases of symptomatic COVID-19 cases throughout 8 countries. Study endpoint was moderate and severe COVID-19 at 28 days post-vaccination among all volunteers.

Overall, the results indicate that the J&J vaccine is 66% effective for the prevention of moderate and severe illness, and was shown to be effective against emerging viral variants at day 28. Level of protection varied based on geographical location:

  • United States: 72%
  • Latin American countries: 66%
  • South Africa: 57%

The vaccine was 85% effective in preventing severe or critical COVID-19 across all geographical regions. It also demonstrated complete protection against COVID-19 related hospitalization and death at day 28 post-vaccination.2

Protection was generally consistent across race, age groups, and all variants and regions studied; this is particularly relevant in South Africa, where over 95% of infections were from the B.1.351 lineage.

The analyses reported 3 deaths in the vaccine group (0 related to COVID-19) and 16 deaths in the placebo group (5 related to COVID-19).


1. Janssen investigational COVID-19 vaccine: interim analysis of phase 3 clinical data released. National Institute of Health. January 29, 2021. Accessed February 9, 2021. https://www.nih.gov/news-events/news-releases/janssen-investigational-covid-19-vaccine-interim-analysis-phase-3-clinical-data-released

2. Johnson & Johnson announces single-shot Janssen COVID-19 vaccine candidate met primary endpoints in interim analysis of its phase 3 ENSEMBLE trial. Johnson & Johnson. January 29, 2021. Accessed February 9, 2021. https://www.jnj.com/johnson-johnson-announces-single-shot-janssen-covid-19-vaccine-candidate-met-primary-endpoints-in-interim-analysis-of-its-phase-3-ensemble-trial