Percorrer por autor "Holm Hansen, Christian"
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- Relative vaccine effectiveness against COVID-19 hospitalisation in persons aged ≥ 65 years: results from a VEBIS network, Europe, October 2021 to July 2023Publication . Fontán-Vela, Mario; Kissling, Esther; Nicolay, Nathalie; Braeye, Toon; Van Evercooren, Izaak; Holm Hansen, Christian; Emborg, Hanne-Dorthe; Fabiani, Massimo; Mateo-Urdiales, Alberto; AlKerwi, Ala'a; Schmitz, Susanne; Castilla, Jesús; Martínez-Baz, Iván; de Gier, Brechje; Hahné, Susan; Meijerink, Hinta; Starrfelt, Jostein; Nunes, Baltazar; Caetano, Constantino; Derrough, Tarik; Nardone, Anthony; Monge, Susana; VEBIS-Lot 4 working groupSince 2021, the Vaccine Effectiveness, Burden and Impact Studies of coronavirus disease 2019 (COVID-19) and influenza (VEBIS) project monitors vaccine effectiveness (VE) in real-world conditions to inform vaccination programmes in the European Union/European Economic Area (EU/EEA) countries [1]. One project aims to monitor real-time COVID-19 VE using electronic health registries (EHR) in multiple countries, with initial findings previously published [2-4]. We report pooled VE results against hospitalisation due to COVID-19 by number of doses received and time since vaccination in a community-dwelling resident population aged ≥ 65 years between October 2021 and July 2023.
- Unmeasured confounding and misclassification in studies estimating vaccine effectiveness against hospitalisation and death using electronic health records (EHRs): an evaluation of a multi-country European retrospective cohort studyPublication . Humphreys, James; Nicolay, Nathalie; Braeye, Toon; Van Evercooren, Izaak; Holm Hansen, Christian; Moustsen-Helms, Ida Rask; Sacco, Chiara; Mateo-Urdiales, Alberto; Castilla, Jesús; Martínez-Baz, Iván; Machado, Ausenda; Soares, Patricia; de Gier, Brechje; Meijerink, Hinta; Monge, Susana; Bacci, Sabrina; Nunes, Baltazar; VEBIS-EHR working groupBackground: Electronic health record (EHR)-based observational studies can rapidly provide real-world data on vaccine effectiveness (VE), though EHR data may be prone to misclassification and unmeasured confounding. Methods: In VEBIS-EHR, a retrospective multi-country COVID-19 VE cohort study, we examined unmeasured confounding using a negative control outcome (death not related to COVID-19) and misclassification due to timing of data extraction. The evaluation spanned two periods (November-December 2023, January-February 2024), encompassing up to 18.7 million individuals across six EU/EEA countries. Vaccine confounding-adjusted hazard ratios (aHRs) were pooled using random-effects meta-analysis. Results: aHRs against non-COVID-19 mortality ranged from 0.35 (95% CI: 0.28-0.44) to 0.70 (0.66-0.73) when comparing vaccinated versus unvaccinated. Delaying EHR data extraction modestly increased the capture of outcome and exposure events, with some variation by vaccination status. Site-level fluctuations in aHRs did not meaningfully alter the overall pooled VE, suggesting stable estimates despite misclassification related to extraction timing. Conclusions: We observed some evidence of unmeasured confounding when using non-COVID-19 deaths as a negative outcome, though the specificity of our negative control must be considered. This result may suggest overestimation of VE, but also the need for further analysis with more specific negative control outcomes and confounding-adjustment techniques. Addressing such confounding using richer data sources and more refined approaches remains critical to ensure accurate, timely VE estimates based on retrospective cohorts constructed using registry data. Extending the delay between the end of observation and data extraction modestly improves the completeness of exposure and outcome data, with limited effect on pooled VE estimates.