Single-dose Ad26.COV2.S vaccine provides moderate protection against Covid-19 related outcomes

1. One dose of Ad26.COV2.S (Johnson & Johnson) provided some protection against moderate to severe Covid-19-related infection and medical intervention.

2. The one dose of Ad26.COV2.S was shown to provide some protection against death for 6 months or longer.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Among other options in vaccines against SARS-CoV-2 (Covid-19), Johnson & Johnson-Janssen produced a recombinant adenoviral 26 (Ad26)-based vaccine expressing the SARS-CoV-2 spike protein. This study presents the final analysis of the phase 3 ENSEMBLE trial to assess its efficacy. Healthy, recruited participants were randomized in a 1:1 ratio to receive either single-dose Ad26.COV2.S or placebo. The primary endpoint assessed was vaccine efficacy against moderate to severe Covid-19 infection either 14 days or 28 days after administration. Safety, including serious and suspected adverse events, was assessed as a secondary endpoint. Vaccine efficacy was calculated using exact Poisson regression. The study found that patients were vaccinated with Ad26.COV2.S had vaccine efficacy against moderate to severe Covid-19 outcomes at both 14 and 28 days after administration, with similar efficacy against different strains. Compared to the placebo group, vaccinated patients also had increased protection against incidence of medical intervention related to Covid-19, and Covid-19 related death for 6 months. Patients receiving Ad26.COV2.S also only experiences mild to moderate adverse events. Taken together, the Ad26.COV2.S vaccine demonstrates good efficacy against moderate to severe outcomes of Covid-19 that wanes over time. Limitations of this study primarily revolve around the lack of data for the Omicron variant, which now represents the majority of cases at this stage of the pandemic.

Click to read the study in NEJM 

Relevant Reading: Ad26 vector-based COVID-19 vaccine encoding a prefusion-stabilized SARS-CoV-2 Spike immunogen induces potent humoral and cellular immune responses

In-Depth [randomized controlled trial]: In this ongoing, double-blind, phase 3 randomized control trial named ENSEMBLE, the primary objective was to evaluate the vaccine efficacy of the single-dose Ad26.COV2.S vaccine against SARS-CoV-2. 43,788 recruited participants were randomized in a 1:1 ratio to receive either one dose of Ad26.COV2.S intramuscular or saline placebo, respectively. Primary endpoints were assessed for PCR-confirmed Covid-19 infection, moderate to severe disease caused by Covid-19, medical intervention due to Covid-19, and Covid-19 related deaths at 14 and 28 days after administration. Vaccine efficacy for these outcomes was calculated using Exact Poisson regression while cumulative incidence over time was estimated using Kaplan-Meier survival curves. Safety with respect to the incidence of adverse events was assessed as a secondary outcome. The study found that the vaccine efficacy against symptomatic Covid-19 infection was 52.4% (95% Confidence Interval [CI], 46.6 – 57.6) at 28 days after administration, and protection lasted approximately 6 months before the modest decline. Protection against moderate to severe Covid-19 infection was 52.9% (95% CI, 47.1 – 58.1), 75.6% (95% CI, 54.3 – 88.0) against Covid-19 requiring medical intervention, and 82.8% (95% CI, 40.5 – 96.8) against Covid-19 related death. These outcomes were similar against other viral strains at 44.4% (95% CI, 34.6 – 52.8) against all strains other than the reference strain. For safety, mild-to-moderate adverse effects were reported for both groups with only 1% of the vaccine group suffering adverse events of grade 3 or higher. Overall, the data support the vaccine efficacy of the Ad26.COV2.S and its use in the Covid-19 pandemic; however, data on the Omicron variant, which makes up the majority of current cases, is required.

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