Analysis of the Effectiveness of the Ad26.COV2.S Adenoviral Vector Vaccine for Preventing COVID-19 | Infectious Diseases | JAMA Network Open | JAMA Network
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    Original Investigation
    Public Health
    November 2, 2021

    Analysis of the Effectiveness of the Ad26.COV2.S Adenoviral Vector Vaccine for Preventing COVID-19

    Author Affiliations
    • 1nference, Cambridge, Massachusetts
    • 2nference Labs, Murgesh Pallya, Bengaluru, Karnataka, India
    • 3Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota
    JAMA Netw Open. 2021;4(11):e2132540. doi:10.1001/jamanetworkopen.2021.32540
    Key Points

    Question  How effective is the Ad26.COV2.S adenoviral vector vaccine from Johnson & Johnson at preventing SARS-CoV-2 infection?

    Findings  This comparative effectiveness research study found that, through large-scale longitudinal retrospective curation of electronic health records from the multistate Mayo Clinic Health System, the Ad26.COV2.S vaccine had an effectiveness of 74%.

    Meaning  This study suggests that a single dose of the Ad26.COV2.S vaccine appears highly effective at preventing SARS-CoV-2 infection.


    Importance  Continuous assessment of the effectiveness and safety of the US Food and Drug Administration–authorized SARS-CoV-2 vaccines is critical to amplify transparency, build public trust, and ultimately improve overall health outcomes.

    Objective  To evaluate the effectiveness of the Johnson & Johnson Ad26.COV2.S vaccine for preventing SARS-CoV-2 infection.

    Design, Setting, and Participants  This comparative effectiveness research study used large-scale longitudinal curation of electronic health records from the multistate Mayo Clinic Health System (Minnesota, Arizona, Florida, Wisconsin, and Iowa) to identify vaccinated and unvaccinated adults between February 27 and July 22, 2021. The unvaccinated cohort was matched on a propensity score derived from age, sex, zip code, race, ethnicity, and previous number of SARS-CoV-2 polymerase chain reaction tests. The final study cohort consisted of 8889 patients in the vaccinated group and 88 898 unvaccinated matched patients.

    Exposure  Single dose of the Ad26.COV2.S vaccine.

    Main Outcomes and Measures  The incidence rate ratio of SARS-CoV-2 infection in the vaccinated vs unvaccinated control cohorts, measured by SARS-CoV-2 polymerase chain reaction testing.

    Results  The study was composed of 8889 vaccinated patients (4491 men [50.5%]; mean [SD] age, 52.4 [16.9] years) and 88 898 unvaccinated patients (44 748 men [50.3%]; mean [SD] age, 51.7 [16.7] years). The incidence rate ratio of SARS-CoV-2 infection in the vaccinated vs unvaccinated control cohorts was 0.26 (95% CI, 0.20-0.34) (60 of 8889 vaccinated patients vs 2236 of 88 898 unvaccinated individuals), which corresponds to an effectiveness of 73.6% (95% CI, 65.9%-79.9%) and a 3.73-fold reduction in SARS-CoV-2 infections.

    Conclusions and Relevance  This study’s findings are consistent with the clinical trial–reported efficacy of Ad26.COV2.S and the first retrospective analysis, suggesting that the vaccine is effective at reducing SARS-CoV-2 infection, even with the spread of variants such as Alpha or Delta that were not present in the original studies, and reaffirm the urgent need to continue mass vaccination efforts globally.