Half Dose ChAdOx1 nCoV-19 Vaccine Was Equivalent to Full Doses to Reduce Moderate and Severe COVID-19 Cases

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Background: During the COVID-19 emergency, different vaccination strategies were developed to combat moderate or severe cases and avoid millions of deaths worldwide. Among the vaccine protocols studied for COVID-19, the Viana Project Study has demonstrated the effectiveness of primary vaccination with a half dose of ChAdOx1 nCoV-19 for preventing new cases in short-term follow-up. This study evaluates the effectiveness of a half dose (HD) of ChAdOx1 nCoV-19 in the primary immunization protocol (up to 2 doses) in reducing moderate and severe cases, hospitalizations, and deaths when compared to the administration of full doses (FD) after a long-term follow-up. Methods: We evaluated the immunization data from 29,469 Viana Project participants between January 2021 and November 2022 that received a HD or FD vaccine and crossed this information with their medical records to identify those who developed moderate or severe COVID-19 cases. All participants were classified into four groups according to their immunization status and followed 500 days after the last vaccine administration. Findings: The propensity-score matching analysis indicate that the administration of the two HD ChAdOx1 nCoV-19 vaccine was equivalent to the use of two FD to reduce moderate and severe COVID-19 cases and the relative risk of being infected and developing moderate or severe conditions after the administration of at least one HD or FD was similar 150 or 500 days after the administration of the respective immunizers. Interpretation: Administering two HD can be used safely as a cost-effective alternative to the primary immunization protocol. Funding: This study was supported by Instituto de Ensino, Pesquisa e Inovação (ICEPi)/Secretaria de Estado da Saúde do Espírito Santo (SESA), Ministério da Saúde do Brasil, Fundação Oswaldo Cruz (FIOCRUZ), Hospital Universitário Cassiano Antônio Moraes da Universidade Federal do Espírito Santo (HUCAM-UFES), Empresa Brasileira de Serviços Hospitalares (EBSERH), Prefeitura Municipal de Viana, and Organização Pan-Americanca da Saúde (OPAS). In addition, the study was carried out by students and professors enrolled in the Post-graduation courses: Saúde Coletiva (PPGSC/UFES), Ciências da Saúde (IRR/FIOCRUZ), all supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). This study was supported by the "Scientific and Technological Development of Digital Health Solutions - Regula e Confia" project (Grant #9684.11.1222 - ICEPi/ES). Declaration of Interest: The authors declare no conflict of interest. Ethical Approval: The studies involving human participants were reviewed and approved by National Research Ethics Committee (CONEP, Protocol No. 4.752.775/2021); and the Ethics Review Committee of the Pan American Health Organization (PAHOERC, Protocol No. 0367.02/2021). In addition, the patients/ participants provided their written informed consent to participate in this study.
Epistemonikos ID: 4da1d0c1ec29a839550cbc1f2062c182694b01c9
First added on: Jun 25, 2023