![]() This bias persists when all infected and uninfected vaccinated and unvaccinated are observed (dark blue and red). An example of a mechanism of bias for (1) is differences in exposure (arrows), where higher exposure for vaccinated individuals compared to unvaccinated individuals produces higher infection levels among vaccinated. Sources (or mechanisms) of bias capable of producing false-negative VE against infection either affect (1) true levels of infection by vaccination status or (2) observed levels of infection by vaccination status. All rights reserved.īias classification framework for observed negative VE against infection. We conclude by discussing the use of suspected false-negative VE measurements as a signal to interrogate the estimates (quantitative bias analysis) and to discuss potential biases when communicating real-world immunity research.īias Cohort-studies Immunity SARS-CoV-2 Test-negative-design.Ĭopyright © 2023 The Author(s). In this perspective, we first outline the different mechanisms of bias that could lead to false-negative VE measurements and then discuss their ability to potentially influence other protection measurements. Although negative VE is more likely to arise when true biological efficacy is generally low and biases are large, positive VE measurements can also be subject to the same mechanisms of bias. However, current observations of negative VE likely stem from the presence of various biases (e.g., exposure differences, testing differences). ![]() Since the emergence of the SARS-CoV-2 Omicron variant, multiple observational studies have reported negative vaccine effectiveness (VE) against infection, symptomatic infection, and even severity (hospitalization), potentially leading to an interpretation that vaccines were facilitating infection and disease. ![]() Michael's Hospital, Unity Health Toronto, Toronto, Canada ICES, Toronto, Canada Epidemiology Division, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada Institute of Medical Science, University of Toronto, Toronto, Canada Institute of Health Policy, Management and Evaluation, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada Department of Medicine, University of Toronto, Toronto, Canada. 4 MAP Centre for Urban Health Solutions, St.3 Public Health Ontario, Toronto, Canada ICES, Toronto, Canada Epidemiology Division, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada Clinical Public Health Division, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada Centre for Vaccine Preventable Diseases, University of Toronto, Toronto, Canada Department of Family and Community Medicine, University of Toronto, Toronto, Canada University Health Network, Toronto, Canada. ![]() Electronic address: 2 British Columbia Centre for Disease Control, Vancouver, Canada Health Sciences, Simon Fraser University, Burnaby, Canada. Michael's Hospital, Unity Health Toronto, Toronto, Canada.
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