Journal of Vaccine Research 2024, Vol.14, No.5, 231-242 http://medscipublisher.com/index.php/jvr 231 Review Article Open Access COVID-19 Vaccines and Variants: Assessing Protection Levels Across Different Strains TianZhao CanSino Biologics Inc., Tianjin, 300462, Tianjin, China Corresponding email: tianzhao@hotmail.com Journal of Vaccine Research, 2024, Vol.14, No.5 doi: 10.5376/jvr.2024.14.0022 Received: 25 Jul., 2024 Accepted: 10 Sep., 2024 Published: 20 Sep., 2024 Copyright © 2024 Zhao, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Zhao T., 2024, COVID-19 vaccines and variants: assessing protection levels across different strains, Journal of Vaccine Research, 14(5): 231-242 (doi: 10.5376/jvr.2024.14.0022) Abstract The emergence of various SARS-CoV-2 variants has posed significant challenges to the efficacy of COVID-19 vaccines. This stdy assesses the protection levels offered by different COVID-19 vaccines against multiple SARS-CoV-2 variants, including Alpha (B.1.1.7), Beta (B.1.351), Gamma, and Delta (B.1.617.2). The ChAdOx1 nCoV-19 (AZD1222) vaccine demonstrated reduced neutralization activity against the B.1.1.7 variant but maintained clinical efficacy. Full vaccination with mRNA vaccines showed high effectiveness against the Alpha variant and moderate effectiveness against Beta/Gamma and Delta variants, while partial vaccination was less effective. The BNT162b2 and ChAdOx1 nCoV-19 vaccines exhibited lower effectiveness after one dose against the Delta variant compared to the Alpha variant, but two doses provided substantial protection. The ChAdOx1 nCoV-19 vaccine showed limited efficacy against mild-to-moderate COVID-19 caused by the B.1.351 variant. Overall, while vaccines have significantly reduced the incidence and severity of COVID-19, the emergence of new variants necessitates ongoing evaluation of vaccine efficacy and potential updates to vaccine formulations. Keywords COVID-19 vaccines; SARS-CoV-2 variants; Vaccine efficacy; Neutralization activity; Immunogenicity 1 Introduction The COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has led to an unprecedented global health crisis. In response, several vaccines have been developed and deployed at an extraordinary pace. Among the most prominent are the mRNA-based vaccines, such as BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna), which have demonstrated high efficacy in preventing symptomatic COVID-19 in clinical trials (Baden et al., 2020; Thompson et al., 2021). These vaccines work by encoding the spike protein of SARS-CoV-2, thereby eliciting an immune response that provides protection against the virus (Mulligan et al., 2020). Other vaccines, including viral vector vaccines like ChAdOx1 (AstraZeneca) and Ad26.COV2.S (Johnson and Johnson), have also been widely used and shown to be effective (Lauring et al., 2022; Zhang et al., 2023). The emergence of SARS-CoV-2 variants, such as Alpha (B.1.1.7), Beta (B.1.351), Delta (B.1.617.2), and Omicron (B.1.1.529), has raised concerns about the continued efficacy of existing vaccines. These variants have mutations that may affect the virus's transmissibility and its ability to evade the immune response induced by vaccination (Mulligan et al., 2020; Chemaitelly et al., 2021). For instance, the Delta variant has been associated with reduced vaccine effectiveness, necessitating booster doses to maintain high levels of protection (Mulligan et al., 2020). Similarly, the Omicron variant has shown a significant reduction in neutralization by antibodies generated from previous infection or vaccination, although booster doses have been shown to enhance protection (Mulligan et al., 2020; Fiolet et al., 2021). The effectiveness of vaccines against these variants varies, with mRNA vaccines generally showing higher efficacy compared to other types (Haas et al., 2021; Zeng et al., 2021). This study provides a comprehensive assessment of the protection levels offered by COVID-19 vaccines against different SARS-CoV-2 variants. By synthesizing data from various studies, to understand the extent to which these vaccines remain effective in the face of emerging variants and to identify any gaps in protection that may need to be addressed through booster doses or new vaccine formulations. Understanding the impact of variants on
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