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Reconstruction of a large-scale outbreak of SARS-CoV-2 infection in Iceland informs vaccination strategies

Hjorleifsson, Kristjan E. and Rognvaldsson, Solvi and Jonsson, Hakon and Agustsdottir, Arna B. and Andresdottir, Margret and Birgisdottir, Kolbrun and Eiriksson, Ogmundur and Eythorsson, Elias S. and Fridriksdottir, Run and Georgsson, Gudmundur and Gudmundsson, Kjartan R. and Gylfason, Arnaldur and Haraldsdottir, Gudbjorg and Jensson, Brynjar O. and Jonasdottir, Adalbjorg and Jonasdottir, Aslaug and Josefsdottir, Kamilla S. and Kristinsdottir, Nina and Kristjansdottir, Borghildur and Kristjansson, Thordur and Magnusdottir, Droplaug N. and Palsson, Runolfur and le Roux, Louise and Sigurbergsdottir, Gudrun M. and Sigurdsson, Asgeir and Sigurdsson, Martin I. and Sveinbjornsson, Gardar and Thorarensen, Emil Aron and Thorbjornsson, Bjarni and Thordardottir, Marianna and Helgason, Agnar and Holm, Hilma and Jonsdottir, Ingileif and Jonsson, Frosti and Magnusson, Olafur T. and Masson, Gisli and Norddahl, Gudmundur L. and Saemundsdottir, Jona and Sulem, Patrick and Thorsteinsdottir, Unnur and Gudbjartsson, Daniel F. and Melsted, Pall and Stefansson, Kari (2022) Reconstruction of a large-scale outbreak of SARS-CoV-2 infection in Iceland informs vaccination strategies. Clinical Microbiology and Infection, 28 (6). pp. 852-858. ISSN 1198-743X. PMCID PMC8849849. doi:10.1016/j.cmi.2022.02.012.

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Objectives: The spread of SARS-CoV-2 is dependent on several factors, both biological and behavioural. The effectiveness of nonpharmaceutical interventions can be attributed largely to changes in human behaviour, but quantifying this effect remains challenging. Reconstructing the transmission tree of the third wave of SARS-CoV-2 infections in Iceland using contact tracing and viral sequence data from 2522 cases enables us to directly compare the infectiousness of distinct groups of persons. Methods: The transmission tree enables us to model the effect that a given population prevalence of vaccination would have had on the third wave had one of three different vaccination strategies been implemented before that time. This allows us to compare the effectiveness of the strategies in terms of minimizing the number of cases, deaths, critical cases, and severe cases. Results: We found that people diagnosed outside of quarantine (Ȓ = 1.31) were 89% more infectious than those diagnosed while in quarantine (Ȓ = 0.70) and that infectiousness decreased as a function of time spent in quarantine before diagnosis, with people diagnosed outside of quarantine being 144% more infectious than those diagnosed after ≥3 days in quarantine (Ȓ = 0.54). People of working age, 16 to 66 years (Ȓ = 1.08), were 46% more infectious than those outside of that age range (Ȓ = 0.74). Discussion: We found that vaccinating the population in order of ascending age or uniformly at random would have prevented more infections per vaccination than vaccinating in order of descending age, without significantly affecting the expected number of deaths, critical cases, or severe cases.

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Hjorleifsson, Kristjan E.0000-0002-7851-1818
Additional Information:© 2022 European Society of Clinical Microbiology and Infectious Diseases. Published by Elsevier Ltd. All rights reserved. Received 29 June 2021, Revised 19 January 2022, Accepted 5 February 2022, Available online 17 February 2022. Author contributions: K.E.H. and S.R. contributed equally to this article. KEH, SR, PM, and KS designed the study and interpreted the results. ABA, MA, KB, GH, AdJ, AsJ, NK, BK, DNM, LLR, GMS, AS, FJ, OTM, GLN, and JS planned and performed the laboratory work. ESE, RP, MIS, and MT performed the data collection. KEH, SR, HJ, ESE, RF, GG, KRG, AG, BOJ, KSJ, TK, RP, MIS, GS, EAT, BT, MT, AH, HH, IJ, GM, PS, UT, and PM performed the data curation. KEH, SR, HJ, OE, DFG, and PM performed the statistical and bioinformatics analyses. KEH, SR, PM, and KS drafted the manuscript. All authors contributed to the final version of the paper. Ethics statement: This study was approved by the National Bioethics Committee of Iceland (approval no. VSN-20-070) after review by the Icelandic Data Protection Authority. Consent was not required from the participants in the study. Transparency declaration: All authors declare no conflicts of interest. No external funding.
Subject Keywords:COVID-19; Outbreak reconstruction; SARS-CoV-2; Transmission tree; Vaccination strategy
Issue or Number:6
PubMed Central ID:PMC8849849
Record Number:CaltechAUTHORS:20220228-862133400
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Official Citation:Kristjan E. Hjorleifsson, Solvi Rognvaldsson, Hakon Jonsson, Arna B. Agustsdottir, Margret Andresdottir, Kolbrun Birgisdottir, Ogmundur Eiriksson, Elias S. Eythorsson, Run Fridriksdottir, Gudmundur Georgsson, Kjartan R. Gudmundsson, Arnaldur Gylfason, Gudbjorg Haraldsdottir, Brynjar O. Jensson, Adalbjorg Jonasdotti, Aslaug Jonasdottir, Kamilla S. Josefsdottir, Nina Kristinsdottir, Borghildur Kristjansdottir, Thordur Kristjansson, Droplaug N. Magnusdottir, Runolfur Palsson, Louise le Roux, Gudrun M. Sigurbergsdottir, Asgeir Sigurdsson, Martin I. Sigurdsson, Gardar Sveinbjornsson, Emil Aron Thorarensen, Bjarni Thorbjornsson, Marianna Thordardottir, Agnar Helgason, Hilma Holm, Ingileif Jonsdottir, Frosti Jonsson, Olafur T. Magnusson, Gisli Masson, Gudmundur L. Norddahl, Jona Saemundsdottir, Patrick Sulem, Unnur Thorsteinsdottir, Daniel F. Gudbjartsson, Pall Melsted, Kari Stefansson, Reconstruction of a large-scale outbreak of SARS-CoV-2 infection in Iceland informs vaccination strategies, Clinical Microbiology and Infection, Volume 28, Issue 6, 2022, Pages 852-858, ISSN 1198-743X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113631
Deposited By: Tony Diaz
Deposited On:28 Feb 2022 17:38
Last Modified:31 May 2022 17:14

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