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PLoS One . Effectiveness of ChAdOx1 nCoV-19 and BBIBP-CorV vaccines against COVID-19-associated hospitalisation and death in the Seychelles infected adult population

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  • PLoS One . Effectiveness of ChAdOx1 nCoV-19 and BBIBP-CorV vaccines against COVID-19-associated hospitalisation and death in the Seychelles infected adult population

    PLoS One


    . 2024 Apr 5;19(4):e0299747.
    doi: 10.1371/journal.pone.0299747. eCollection 2024. Effectiveness of ChAdOx1 nCoV-19 and BBIBP-CorV vaccines against COVID-19-associated hospitalisation and death in the Seychelles infected adult population

    Sylvie Nadine Theresa Pool 1 , Emelyn Helen Shroff 2 , Agnes Chetty 3 , Lara Lewis 4 , Yende-Zuma Nonhlanhla 4 , Salim S Abdool Karim 4



    AffiliationsAbstract

    Background: The Seychelles COVID-19 vaccination campaign was initiated using two different vaccines during the first wave of the pandemic in 2021. This observational study estimated vaccine effectiveness against severe outcomes (hospitalisation and/or death) from individuals infected with COVID-19 in the Seychelles adult population during Beta and Delta variant transmission.
    Methods: This nationwide retrospective cohort study included all Seychellois residents aged ≥ 18 years who tested positive by RT-PCR or rapid antigen test for COVID-19 between January 25, 2021, and June 30, 2021. We measured the relative risk (RR) of laboratory-confirmed SARS-CoV-2 hospitalisation and/or death among individuals partially or fully vaccinated with ChAdOx1 nCoV-19 (SII Covishield) or BBIBP-CorV (Sinopharm) vaccines compared to unvaccinated individuals using modified Poisson regression. Controlling for age, gender and calendar month, vaccine effectiveness was estimated as 1-RR ≥14 days after the first dose and ≥7 days after the second dose for each available vaccine versus an unvaccinated control group.
    Results: A total of 12,326 COVID-19 infections were reported in adult Seychellois residents between January 25, 2021, and June 30, 2021. Of these, 1,287 individuals received one dose of either BBIBP-CorV (Sinopharm) or ChAdOx1-nCoV-19 (SII Covishield) vaccine, and 5,225 individuals received two doses. Estimated adjusted effectiveness of two doses of either Sinopharm or SII Covishield was high, at 70% (95% CI 58%-78%) and 71% (95% CI 62%-78%) respectively. Sinopharm maintained high levels of protection against severe outcomes in partially vaccinated individuals at 61% (95% CI 36%-76%), while the effectiveness of one dose of SII Covishield was low at 29% (95% CI 1%-49%).
    Conclusions: This observational study demonstrated high levels of protection of two doses of two vaccine types against severe outcomes of COVID-19 during the first wave of the pandemic driven by Beta (B.1.351) and Delta (B.1.617.2) variant predominance. One dose of ChAdOx1-nCoV-19 (Covishield SII) was found to be inadequate in protecting the general adult population against hospitalisation and/or death from COVID-19.


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