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Theoretical Framework for Retrospective Studies of the Effectiveness of SARS-CoV-2 Vaccines.

ABSTRACT: Observational studies of the effectiveness of vaccines to prevent COVID-19 are needed to inform real-world use. Such studies are now underway amid the ongoing rollout of SARS-CoV-2 vaccines globally. Although traditional case-control and test-negative design studies feature prominently among strategies used to assess vaccine effectiveness, such studies may encounter important threats to validity. Here, we review the theoretical basis for estimation of vaccine direct effects under traditional case-control and test-negative design frameworks, addressing specific natural history parameters of SARS-CoV-2 infection and COVID-19 relevant to these designs. Bias may be introduced by misclassification of cases and controls, particularly when clinical case criteria include common, nonspecific indicators of COVID-19. When using diagnostic assays with high analytical sensitivity for SARS-CoV-2 detection, individuals testing positive may be counted as cases even if their symptoms are due to other causes. The traditional case-control design may be particularly prone to confounding due to associations of vaccination with healthcare-seeking behavior or risk of infection. The test-negative design reduces but may not eliminate this confounding, for instance, if individuals who receive vaccination seek care or testing for less-severe illness. These circumstances indicate the two study designs cannot be applied naively to datasets gathered through public health surveillance or administrative sources. We suggest practical strategies to reduce bias in vaccine effectiveness estimates at the study design and analysis stages.

SUBMITTER: Lewnard JA

PROVIDER: S-EPMC8168935 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundSeveral vaccines with demonstrated efficacy for coronavirus disease 2019 (Covid-19) are available. The purpose of this study was to evaluate the COVID mRNA based and adenovector based vaccines' differential effectiveness during the time of circulation of the Delta variant and determine what impact this would have on population health and cost effectiveness.MethodsWe used de-identified claims in a research database that included vaccination status and Covid-positivity status. Individuals ≥18 years, fully vaccinated with Ad26.COV2·S/J&J/Janssen, mRNA-1273/Moderna, or BNT162b2/Pfizer-BioNTech by September 30, 2021, were included. Outcomes were SARS-CoV-2-infection, emergency department visits, outpatient visits, inpatient hospitalizations, intensive care unit (ICU) transfers, death, and hospice transfers through September 30, 2021.ResultsAmong ∼6.5 million fully vaccinated individuals in the UHC Medicare Advantage and our commercially insured research database, mRNA-1273 performed better than BNT162b2 for infection, composite-hospitalization (hospitalization/ICU transfer/hospice transfer/death), and composite-ICU transfer (ICU transfer/hospice transfer/death) caused by B.1.612.7 (delta) variant infection. 26 CE.COV2.S performed worse than BNT162b2 for infection, composite-hospitalization, and composite-ICU transfers. The number needed to vaccinate (NNV) with mRNA1273 to prevent one hospitalization at 90 days was 3130 compared to 26 CE.COV2·S and 15,472 compared to BNT162b2. The NNV with mRNA1273 to prevent one ICU transfer at 90 days was 6358 compared to 26 CE.COV2·S and 34,279 compared to BNT162b2. For every one million individuals vaccinated with BNT162b compared to mRNA-1273, the approximate incremental inpatient cost would be $405,000 and the approximate incremental ICU cost would be $662,000.ConclusionsThe two-dose mRNA vaccines' effectiveness significantly exceeded the single-dose Ad26.COV2·S vaccine's effectiveness from population health and cost-effectiveness perspectives. The mRNA1273 vaccine showed slightly more effectiveness than the BNT162b vaccine.

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Theoretical Framework for Retrospective Studies of the Effectiveness of SARS-CoV-2 Vaccines.

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