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

• Published in: Clinical Microbiology and Infection
• Main Authors: Hjorleifsson, Kristjan E., Rognvaldsson, Solvi, Jonsson, Hakon, Agustsdottir, Arna B., Andresdottir, Margret, Birgisdottir, Kolbrun, Eiriksson, Ogmundur, Eythorsson, Elias S., Fridriksdottir, Run, Georgsson, Gudmundur, Gudmundsson, Kjartan R., Gylfason, Arnaldur, Haraldsdottir, Gudbjorg, Jensson, Brynjar O., Jonasdottir, Adalbjorg, Jonasdottir, Aslaug, Josefsdottir, Kamilla S., Kristinsdottir, Nina, Kristjansdottir, Borghildur, Kristjansson, Thordur, Magnusdottir, Droplaug N., Palsson, Runolfur, le Roux, Louise, Sigurbergsdottir, Gudrun M., Sigurdsson, Asgeir, Sigurdsson, Martin I., Sveinbjornsson, Gardar, Thorarensen, Emil Aron, Thorbjornsson, Bjarni, Thordardottir, Marianna, Helgason, Agnar, Holm, Hilma, Jonsdottir, Ingileif, Jonsson, Frosti, Magnusson, Olafur T., Masson, Gisli, Norddahl, Gudmundur L., Saemundsdottir, Jona, Sulem, Patrick, Thorsteinsdottir, Unnur, Gudbjartsson, Daniel F., Melsted, Pall, Stefansson, Kari
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2022
• Subjects: COVID-19; Outbreak reconstruction; SARS-CoV-2; Transmission tree; Vaccination strategy; Infectious Diseases; Microbiology (medical); General Medicine; Iceland
• Online Access: https://www.ncbi.nlm.nih.gov/pmc/PMC8849849; https://doi.org/10.1016/j.cmi.2022.02.012

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. © 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 ...