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Use of Recently Vaccinated Individuals to Detect Bias in Test-Negative Case-Control Studies of COVID-19 Vaccine Effectiveness.

ABSTRACT: Postauthorization observational studies play a key role in understanding COVID-19 vaccine effectiveness following the demonstration of efficacy in clinical trials. Although bias due to confounding, selection bias, and misclassification can be mitigated through careful study design, unmeasured confounding is likely to remain in these observational studies. Phase III trials of COVID-19 vaccines have shown that protection from vaccination does not occur immediately, meaning that COVID-19 risk should be similar in recently vaccinated and unvaccinated individuals, in the absence of confounding or other bias. Several studies have used the estimated effectiveness among recently vaccinated individuals as a negative control exposure to detect bias in vaccine effectiveness estimates. In this paper, we introduce a theoretical framework to describe the interpretation of such a bias indicator in test-negative studies, and outline strong assumptions that would allow vaccine effectiveness among recently vaccinated individuals to serve as a negative control exposure.

SUBMITTER: Hitchings MDT

PROVIDER: S-EPMC9148635 | biostudies-literature | 2022 Jul

REPOSITORIES: biostudies-literature

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Use of Recently Vaccinated Individuals to Detect Bias in Test-Negative Case-Control Studies of COVID-19 Vaccine Effectiveness.

Hitchings Matt D T MDT Lewnard Joseph A JA Dean Natalie E NE Ko Albert I AI Ranzani Otavio T OT Andrews Jason R JR Cummings Derek A T DAT

Epidemiology (Cambridge, Mass.) 20220401 4

Postauthorization observational studies play a key role in understanding COVID-19 vaccine effectiveness following the demonstration of efficacy in clinical trials. Although bias due to confounding, selection bias, and misclassification can be mitigated through careful study design, unmeasured confounding is likely to remain in these observational studies. Phase III trials of COVID-19 vaccines have shown that protection from vaccination does not occur immediately, meaning that COVID-19 risk shoul ...[more]

PMID: 35384900

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Project description:ObjectivesWe compared the vaccine effectiveness over time of the primary series and booster against infection and severe disease with the Delta, Omicron BA.1, and BA.2 variants in Singapore, an Asian setting with high vaccination coverage.MethodsWe conducted a test-negative case-control study on all adult residents in Singapore who underwent PCR testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in acute hospitals. Individuals with a negative PCR from 1 September, 2021, to 30 November, 2021, and 1 December, 2021, to 25 April, 2022, served as controls for the Delta and Omicron variants respectively, and PCR-positive individuals within these two time periods served as cases. Associations between vaccination status and severe SARS-CoV-2 infection and severe disease with the Delta or Omicron variants were measured using Poisson regressions. Vaccine effectiveness was calculated by taking 1 minus risk ratio.ResultsThere were 68 114 individuals comprising 58 495 controls and 9619 cases for the Delta period, of whom 53 093 completed the primary series and 9161 were boosted. For the Omicron period, 104 601 individuals comprising 80 428 controls, 8643 BA.1 cases, and 15 530 BA.2 cases were included, of whom 29 183 and 71 513 were vaccinated with the primary series and boosted, respectively. The primary series provided greater protection against infection with Delta (45%, 95% CI 40-50%) than against infection with Omicron (21%, 95% CI 7-34% for BA.1; 18%, 95% CI 6-29% for BA.2) at <2 months from vaccination. Vaccine effectiveness of the booster was similar against infection with BA.1 (44%, 95% CI 38-50%) and BA.2 (40%, 95% CI 35-40%). Protection against severe disease by the booster for BA.1 (83%, 95% CI 76-88%) and BA.2 (78%, 95% CI 73-82%) was comparable to that by the primary series for Delta (80%, 95% CI 73-85%).ConclusionOur findings support the use of a booster dose to reduce the risk of severe disease and mitigate the impact on the healthcare system in an Omicron-predominant epidemic.

Dataset Information

Use of Recently Vaccinated Individuals to Detect Bias in Test-Negative Case-Control Studies of COVID-19 Vaccine Effectiveness.

Publications

Use of Recently Vaccinated Individuals to Detect Bias in Test-Negative Case-Control Studies of COVID-19 Vaccine Effectiveness.

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