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Effectiveness of COVID-19 vaccines against B.1.617.2 (delta) variant: A systematic review

White, Joseph F (2021) Effectiveness of COVID-19 vaccines against B.1.617.2 (delta) variant: A systematic review. Master Essay, University of Pittsburgh.

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Introduction: The coronavirus disease 2019 (COVID-19) pandemic continues to inflict significant morbidity and mortality globally. The asymmetric distribution of vaccines continues to foment the emergence of more transmissible SARS-CoV-2 variants of concern (VOC). Research has shown a reduction in vaccine effectiveness (VE) against these variants, with the most recent being the B.1.617.2 (Delta) variant. The aim of this systematic review is to synthesize COVID-19 VE estimates and their 95% confidence intervals (95% CI) against SARS-CoV-2 Delta variant infection, symptomatic disease, and hospitalization. An updated synthesis of VE estimates against Delta variant is necessary to inform clinical decision-making, policy decisions, and promote vaccine development to protect against future variants.
Methods: A comprehensive literature search was conducted using the Ovid-MEDLINE database on October 16, 2021. Observational studies examining VE of WHO-approved COVID-19 vaccines were included. The Newcastle-Ottawa Scale (NOS) was used to assess the quality of the non-randomized observational studies included in this review.
Results: Eleven studies met eligibility criteria to be included in the review. Overall VE estimates against SARS-CoV-2 Delta variant infection for WHO-approved vaccines reported in this review ranged from 59% [95% CI: 16, 81.6] to 75% [95% CI: 71, 78]. VE against symptomatic Delta variant infection was reported as 79.6 [76.7, 82.1]. Overall VE against Delta variant hospitalization ranged from 86% [95% CI: 82, 89] to 93% [95% CI: 84, 96]. VE against specific vaccines was also reported.
Conclusions: Studies included in this review provide evidence that VE against the Delta variant of SARS-CoV-2 is less than VE against previous VOC and wild type SARS-CoV-2 for preventing infection, symptomatic disease and hospitalization. This review demonstrates the vital need for continuous surveillance of VE so that vaccine programs are dynamic and adaptable to the epidemiology of COVID-19. Subsequent research is necessary to examine if the primary reason for reduced VE is VOC immune evasion or waning immunity due to time. This review is relevant to public health practice because it can inform how vaccine programs should adapt to the dynamic nature SARS-CoV-2, in measures such recommending booster doses for certain populations.


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Item Type: Other Thesis, Dissertation, or Long Paper (Master Essay)
Status: Unpublished
CreatorsEmailPitt UsernameORCID
White, Joseph Fjfw21@pitt.edujfw21
ContributionContributors NameEmailPitt UsernameORCID
Committee ChairGlynn, Nancyepidnwg@pitt.eduepidnwgUNSPECIFIED
Committee MemberSnyder, Grahamsnydergm3@upmc.eduUNSPECIFIEDUNSPECIFIED
Committee MemberNowalk, Mary Patriciatnowalk@pitt.edutnowalkUNSPECIFIED
Date: 17 December 2021
Date Type: Completion
Number of Pages: 40
Institution: University of Pittsburgh
Schools and Programs: Graduate School of Public Health > Epidemiology
Thesis Type: Master Essay
Refereed: Yes
Date Deposited: 06 Jan 2022 14:18
Last Modified: 06 Jan 2022 14:18


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