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Safety and Efficacy of Single-Dose Ad26.COV2.S Vaccine against Covid-19

Our take —

This interim analysis from a phase 3 randomized, double-blinded, placebo-controlled clinical trial of the Johnson & Johnson/Janssen Pharmaceuticals Ad26.COV2.S COVID-19 vaccine demonstrated that it is effective, particularly at preventing severe-critical COVID-19. The authors noted that, compared to many of the other vaccines currently available, this COVID-19 vaccine can be stored under a broader range of temperatures and requires only a single dose – both of which are important considerations. Given the initial safety concerns raised, ongoing monitoring and transparency in the post-marketing setting will be crucial.

Study design

Randomized Controlled Trial

Study population and setting

This study reports the findings from the phase 3 randomized, double-blinded, placebo-controlled clinical trial of the Johnson & Johnson/Janssen Pharmaceuticals Ad26.COV2.S COVID-19 vaccine. The single-dose vaccine utilizes recombinant, non-replicating adenovirus type 26 as a vector to deliver double-stranded DNA encoding the full-length SARS-CoV-2 spike (S) protein. The trial, which is still ongoing, is underway in multiple Latin American countries, South Africa, and the United States (this study reports data from September 21, 2020 to January 22, 2021). Approximately 40,000 per-protocol participants were included, with half receiving placebo. Vaccine efficacy against moderate to severe-critical COVID-19 was assessed following at least 14 days and at least 28 days after injection.

Summary of Main Findings

468 confirmed symptomatic cases of COVID-19 were recorded overall: 116 in the vaccine group and 348 in the placebo group. This provided estimated vaccine efficacy at least 14 days following injection of 66.9% (76.7% for severe-critical disease). Vaccine efficacy at least 28 days following injection was 66.1% (85.4% for severe-critical disease). Overall vaccine efficacy against asymptomatic infection with SARS-CoV-2 was estimated at 65.5% based on serological testing throughout the study.

Study Strengths

The study population was large, diverse, and included many patients with comorbidities. Inclusion of estimates for vaccine efficacy against asymptomatic SARS-CoV-2 infection is extremely helpful.

Limitations

The estimated vaccine efficacy against asymptomatic SARS-CoV-2 infection was based on serological testing of participants 71 days after injection to assess for antibodies against the nucleocapsid (N) protein (which would only be present following natural infection, since the vaccine would only induce antibodies against S). However, those with ‘unknown’ baseline serostatus were also included. Ideally only participants with proven seroconversion (negative to positive) should have been utilized for analysis.

Value added

This is the first peer-reviewed report of the phase 3 clinical trial results for the Johnson & Johnson/Janssen Pharmaceuticals Ad26.COV2.S COVID-19 vaccine.

This review was posted on: 14 May 2021