Projected resurgence of COVID-19 in the United States in July-December 2021 resulting from the increased transmissibility of the Delta variant and faltering vaccination

  1. Shaun Truelove  Is a corresponding author
  2. Claire P Smith
  3. Michelle Qin
  4. Luke C Mullany
  5. Rebecca K Borchering
  6. Justin Lessler
  7. Katriona Shea
  8. Emily Howerton
  9. Lucie Contamin
  10. John Levander
  11. Jessica Salerno
  12. Harry Hochheiser
  13. Matt Kinsey
  14. Kate Tallaksen
  15. Shelby Wilson
  16. Lauren Shin
  17. Kaitlin Rainwater-Lovett
  18. Joseph C Lemairtre
  19. Juan Dent Hulse
  20. Joshua Kaminsky
  21. Elizabeth C Lee
  22. Javier Perez-Saez
  23. Alison Hill
  24. Dean Karlen
  25. Matteo Chinazzi
  26. Jessica T Davis
  27. Kunpeng Mu
  28. Xinyue Xiong
  29. Ana Pastore y Piontti
  30. Alessandro Vespignani
  31. Ajitesh Srivastava
  32. Przemyslaw Porebski
  33. Srinivasan Venkatramanan
  34. Aniruddha Adiga
  35. Bryan Lewis
  36. Brian Klahn
  37. Joseph Outten
  38. Mark Orr
  39. Galen Harrison
  40. Benjamin Hurt
  41. Jiangzhuo Chen
  42. Anil Vullikanti
  43. Madhav Marathe
  44. Stefan Hoops
  45. Parantapa Bhattacharya
  46. Dustin Machi
  47. Shi Chen
  48. Rajib Paul
  49. Daniel Janies
  50. Jean-Claude Thill
  51. Marta Galanti
  52. Teresa K Yamana
  53. Sen Pei
  54. Jeffrey L Shaman
  55. Jessica M Healy
  56. Rachel B Slayton
  57. Matthew Biggerstaff
  58. Michael A Johansson
  59. Michael C Runge
  60. Cecile Viboud
  1. Johns Hopkins University, United States
  2. Harvard University, United States
  3. Johns Hopkins University Applied Physics Laboratory, United States
  4. Pennsylvania State University, United States
  5. University of North Carolina at Chapel Hill, United States
  6. University of Pittsburgh, United States
  7. École Polytechnique Fédérale de Lausanne, Switzerland
  8. University of Victoria, Canada
  9. Northeastern University, United States
  10. University of Southern California, United States
  11. University of Virginia, United States
  12. University of North Carolina at Charlotte, United States
  13. Columbia University Medical Center, United States
  14. Centers for Disease Control and Prevention, United States
  15. United States Geological Survey, United States
  16. National Institutes of Health, United States

Abstract

In Spring 2021, the highly transmissible SARS-CoV-2 Delta variant began to cause increases in cases, hospitalizations, and deaths in parts of the United States. At the time, with slowed vaccination uptake, this novel variant was expected to increase the risk of pandemic resurgence in the US in summer and fall 2021. As part of the COVID-10 Scenario Modeling Hub, an ensemble of nine mechanistic models produced six-month scenario projections for July-December 2021 for the United States. These projections estimated substantial resurgences of COVID-19 across the US resulting from the more transmissible Delta variant, projected to occur across most of the US, coinciding with school and business reopening. The scenarios revealed that reaching higher vaccine coverage in July—December 2021 reduced the size and duration of the projected resurgence substantially, with the expected impacts was largely concentrated in a subset of states with lower vaccination coverage. Despite accurate projection of COVID-19 surges occurring and timing, the magnitude was substantially underestimated 2021 by the models compared with the of the reported cases, hospitalizations, and deaths occurring during July-December, highlighting the continued challenges to predict the evolving COVID-19 pandemic. Vaccination uptake remains critical to limiting transmission and disease, particularly in states with lower vaccination coverage. Higher vaccination goals at the onset of the surge of the new variant were estimated to avert over 1.5 million cases and 21,000 deaths, though may have had even greater impacts, considering the underestimated resurgence magnitude from the model.

Data availability

All model output data are available on the project github at https://github.com/midas-network/covid19-scenario-modeling-hub. Code and data specific to this manuscript has been consolidated into a repository at https://github.com/midas-network/covid19-scenario-modeling-hub/tree/master/paper-source-code/round-7. All data used are publicly available.

The following data sets were generated

Article and author information

Author details

  1. Shaun Truelove

    Bloomberg School of Public Health, Johns Hopkins University, Baltimore, United States
    For correspondence
    shauntruelove@jhu.edu
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-0538-0607
  2. Claire P Smith

    Bloomberg School of Public Health, Johns Hopkins University, Baltimore, United States
    Competing interests
    No competing interests declared.
  3. Michelle Qin

    Harvard University, Cambridge, Massachusetts, United States
    Competing interests
    No competing interests declared.
  4. Luke C Mullany

    Johns Hopkins University Applied Physics Laboratory, Laurel, United States
    Competing interests
    No competing interests declared.
  5. Rebecca K Borchering

    Eberly College of Science, Pennsylvania State University, University Park, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-4309-2913
  6. Justin Lessler

    University of North Carolina at Chapel Hill, Chapel Hill, United States
    Competing interests
    Justin Lessler, has served as an expert witness on cases where the likely length of the pandemic was of issue..
  7. Katriona Shea

    Eberly College of Science, Pennsylvania State University, University Park, United States
    Competing interests
    No competing interests declared.
  8. Emily Howerton

    Eberly College of Science, Pennsylvania State University, University Park, United States
    Competing interests
    No competing interests declared.
  9. Lucie Contamin

    University of Pittsburgh, Pittsburgh, United States
    Competing interests
    No competing interests declared.
  10. John Levander

    University of Pittsburgh, Pittsburgh, United States
    Competing interests
    No competing interests declared.
  11. Jessica Salerno

    University of Pittsburgh, Pittsburgh, United States
    Competing interests
    No competing interests declared.
  12. Harry Hochheiser

    University of Pittsburgh, Pittsburgh, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-8793-9982
  13. Matt Kinsey

    Johns Hopkins University Applied Physics Laboratory, Laurel, United States
    Competing interests
    No competing interests declared.
  14. Kate Tallaksen

    Johns Hopkins University Applied Physics Laboratory, Laurel, United States
    Competing interests
    No competing interests declared.
  15. Shelby Wilson

    Johns Hopkins University Applied Physics Laboratory, Laurel, United States
    Competing interests
    No competing interests declared.
  16. Lauren Shin

    Johns Hopkins University Applied Physics Laboratory, Laurel, United States
    Competing interests
    No competing interests declared.
  17. Kaitlin Rainwater-Lovett

    Johns Hopkins University Applied Physics Laboratory, Laurel, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-8707-7339
  18. Joseph C Lemairtre

    École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
    Competing interests
    No competing interests declared.
  19. Juan Dent Hulse

    Bloomberg School of Public Health, Johns Hopkins University, Baltimore, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-3154-0731
  20. Joshua Kaminsky

    Bloomberg School of Public Health, Johns Hopkins University, Baltimore, United States
    Competing interests
    No competing interests declared.
  21. Elizabeth C Lee

    Bloomberg School of Public Health, Johns Hopkins University, Baltimore, United States
    Competing interests
    No competing interests declared.
  22. Javier Perez-Saez

    Bloomberg School of Public Health, Johns Hopkins University, Baltimore, United States
    Competing interests
    No competing interests declared.
  23. Alison Hill

    Bloomberg School of Public Health, Johns Hopkins University, Baltimore, United States
    Competing interests
    No competing interests declared.
  24. Dean Karlen

    University of Victoria, Victoria, Canada
    Competing interests
    No competing interests declared.
  25. Matteo Chinazzi

    Northeastern University, Boston, United States
    Competing interests
    No competing interests declared.
  26. Jessica T Davis

    Northeastern University, Boston, United States
    Competing interests
    No competing interests declared.
  27. Kunpeng Mu

    Northeastern University, Boston, United States
    Competing interests
    No competing interests declared.
  28. Xinyue Xiong

    Northeastern University, Boston, United States
    Competing interests
    No competing interests declared.
  29. Ana Pastore y Piontti

    Northeastern University, Boston, United States
    Competing interests
    No competing interests declared.
  30. Alessandro Vespignani

    Northeastern University, Boston, United States
    Competing interests
    No competing interests declared.
  31. Ajitesh Srivastava

    University of Southern California, Los Angeles, United States
    Competing interests
    No competing interests declared.
  32. Przemyslaw Porebski

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-8012-5791
  33. Srinivasan Venkatramanan

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
  34. Aniruddha Adiga

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
  35. Bryan Lewis

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-0793-6082
  36. Brian Klahn

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
  37. Joseph Outten

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
  38. Mark Orr

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
  39. Galen Harrison

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
  40. Benjamin Hurt

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
  41. Jiangzhuo Chen

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
  42. Anil Vullikanti

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
  43. Madhav Marathe

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
  44. Stefan Hoops

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
  45. Parantapa Bhattacharya

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
  46. Dustin Machi

    University of Virginia, Charlottesville, United States
    Competing interests
    No competing interests declared.
  47. Shi Chen

    University of North Carolina at Charlotte, Charlotte, United States
    Competing interests
    No competing interests declared.
  48. Rajib Paul

    University of North Carolina at Charlotte, Charlotte, United States
    Competing interests
    No competing interests declared.
  49. Daniel Janies

    University of North Carolina at Charlotte, Charlotte, United States
    Competing interests
    No competing interests declared.
  50. Jean-Claude Thill

    University of North Carolina at Charlotte, Charlotte, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-6651-8123
  51. Marta Galanti

    Environmental Health Sciences, Columbia University Medical Center, New York, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-9060-1250
  52. Teresa K Yamana

    Environmental Health Sciences, Columbia University Medical Center, New York, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-8349-3151
  53. Sen Pei

    Department of Environmental Health Sciences, Columbia University Medical Center, New York, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-7072-2995
  54. Jeffrey L Shaman

    Department of Environmental Health Sciences, Columbia University Medical Center, New York, United States
    Competing interests
    Jeffrey L Shaman, and Columbia University disclose partial ownership of SK Analytics. Discloses consulting for BNI..
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-7216-7809
  55. Jessica M Healy

    COVID-19 Response Team, Centers for Disease Control and Prevention, Atlanta, United States
    Competing interests
    No competing interests declared.
  56. Rachel B Slayton

    COVID-19 Response Team, Centers for Disease Control and Prevention, Atlanta, United States
    Competing interests
    No competing interests declared.
  57. Matthew Biggerstaff

    COVID-19 Response Team, Centers for Disease Control and Prevention, Atlanta, United States
    Competing interests
    No competing interests declared.
  58. Michael A Johansson

    COVID-19 Response Team, Centers for Disease Control and Prevention, Atlanta, United States
    Competing interests
    No competing interests declared.
  59. Michael C Runge

    Eastern Ecological Science Center, United States Geological Survey, Laurel, United States
    Competing interests
    Michael C Runge, reports stock ownership in Becton Dickinson & Co., which manufactures medical equipment used in COVID testing, vaccination, and treatment..
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-8081-536X
  60. Cecile Viboud

    Fogarty International Center, National Institutes of Health, Bethesda, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-3243-4711

Funding

National Science Foundation (2127976)

  • Shaun Truelove
  • Claire P Smith
  • Juan Dent Hulse
  • Joshua Kaminsky
  • Elizabeth C Lee
  • Alison Hill

California Department of Public Health

  • Shaun Truelove
  • Claire P Smith
  • Justin Lessler
  • Juan Dent Hulse
  • Joshua Kaminsky
  • Elizabeth C Lee
  • Javier Perez-Saez

Johns Hopkins University

  • Shaun Truelove
  • Claire P Smith
  • Justin Lessler
  • Juan Dent Hulse
  • Joshua Kaminsky
  • Elizabeth C Lee
  • Javier Perez-Saez
  • Alison Hill

National Institutes of Health (R01GM140564)

  • Justin Lessler

Swiss National Science Foundation (200021--172578))

  • Joseph C Lemairtre

National Institutes of Health (R01GM109718)

  • Przemyslaw Porebski
  • Srinivasan Venkatramanan
  • Aniruddha Adiga
  • Bryan Lewis
  • Brian Klahn
  • Joseph Outten
  • Mark Orr
  • Galen Harrison
  • Benjamin Hurt
  • Jiangzhuo Chen
  • Anil Vullikanti
  • Madhav Marathe
  • Stefan Hoops
  • Parantapa Bhattacharya
  • Dustin Machi

Virginia Department of Health (VDH-21-501-0135)

  • Przemyslaw Porebski
  • Srinivasan Venkatramanan
  • Aniruddha Adiga
  • Bryan Lewis
  • Brian Klahn
  • Joseph Outten
  • Mark Orr
  • Galen Harrison
  • Benjamin Hurt
  • Jiangzhuo Chen
  • Anil Vullikanti
  • Madhav Marathe
  • Stefan Hoops
  • Parantapa Bhattacharya
  • Dustin Machi

National Science Foundation (OAC-1916805,CCF-1918656,CCF-2142997,OAC-2027541,TG-BIO210084)

  • Przemyslaw Porebski
  • Srinivasan Venkatramanan
  • Aniruddha Adiga
  • Bryan Lewis
  • Brian Klahn
  • Joseph Outten
  • Mark Orr
  • Galen Harrison
  • Benjamin Hurt
  • Jiangzhuo Chen
  • Anil Vullikanti
  • Madhav Marathe
  • Stefan Hoops
  • Parantapa Bhattacharya
  • Dustin Machi

Centers for Disease Control and Prevention (75D30119C05935)

  • Przemyslaw Porebski
  • Srinivasan Venkatramanan
  • Aniruddha Adiga
  • Bryan Lewis
  • Brian Klahn
  • Joseph Outten
  • Mark Orr
  • Galen Harrison
  • Benjamin Hurt
  • Jiangzhuo Chen
  • Anil Vullikanti
  • Madhav Marathe
  • Stefan Hoops
  • Parantapa Bhattacharya
  • Dustin Machi

Defense Threat Reduction Agency (S-D00189-15-TO-01-UVA)

  • Przemyslaw Porebski
  • Srinivasan Venkatramanan
  • Aniruddha Adiga
  • Bryan Lewis
  • Brian Klahn
  • Joseph Outten
  • Mark Orr
  • Galen Harrison
  • Benjamin Hurt
  • Jiangzhuo Chen
  • Anil Vullikanti
  • Madhav Marathe
  • Stefan Hoops
  • Parantapa Bhattacharya
  • Dustin Machi

Centers for Disease Control and Prevention (200-2016-91781)

  • Shaun Truelove
  • Claire P Smith
  • Justin Lessler
  • Joseph C Lemairtre
  • Joshua Kaminsky
  • Alison Hill

National Science Foundation (2028301,2126278)

  • Rebecca K Borchering
  • Katriona Shea

University of Virginia

  • Przemyslaw Porebski
  • Srinivasan Venkatramanan
  • Aniruddha Adiga
  • Bryan Lewis
  • Brian Klahn
  • Joseph Outten
  • Mark Orr
  • Galen Harrison
  • Benjamin Hurt
  • Jiangzhuo Chen
  • Anil Vullikanti
  • Madhav Marathe
  • Stefan Hoops
  • Parantapa Bhattacharya
  • Dustin Machi

COVID-19 HPC Consortium

  • Przemyslaw Porebski
  • Srinivasan Venkatramanan
  • Aniruddha Adiga
  • Bryan Lewis
  • Brian Klahn
  • Joseph Outten
  • Mark Orr
  • Galen Harrison
  • Benjamin Hurt
  • Jiangzhuo Chen
  • Anil Vullikanti
  • Madhav Marathe
  • Stefan Hoops
  • Parantapa Bhattacharya
  • Dustin Machi

Amazon Web Services

  • Shaun Truelove
  • Claire P Smith
  • Justin Lessler
  • Joseph C Lemairtre
  • Juan Dent Hulse
  • Joshua Kaminsky
  • Elizabeth C Lee
  • Javier Perez-Saez
  • Alison Hill

Models of Infectious Disease Agent Study (MIDASUP-05)

  • Shi Chen
  • Rajib Paul
  • Daniel Janies
  • Jean-Claude Thill

North Carolina Biotechnology Center

  • Shi Chen
  • Rajib Paul
  • Daniel Janies
  • Jean-Claude Thill

National Institutes of Health (R01AI163023)

  • Marta Galanti
  • Teresa K Yamana
  • Sen Pei
  • Jeffrey L Shaman

Council of State and Territorial Epidemiologists (NU38OT000297)

  • Marta Galanti
  • Teresa K Yamana
  • Sen Pei
  • Jeffrey L Shaman

Morris-Singer Foundation

  • Marta Galanti
  • Teresa K Yamana
  • Sen Pei
  • Jeffrey L Shaman

Huck Institutes of the Life Sciences

  • Katriona Shea
  • Emily Howerton

National Institute of General Medical Sciences (5U24GM132013-02)

  • Lucie Contamin
  • John Levander
  • Jessica Salerno
  • Harry Hochheiser

United States Department of Health and Human Services (75A50121C00003)

  • Luke C Mullany
  • Matt Kinsey
  • Kate Tallaksen
  • Shelby Wilson
  • Lauren Shin
  • Kaitlin Rainwater-Lovett

United States Department of Health and Human Services (6U01IP001137)

  • Jessica T Davis
  • Ana Pastore y Piontti
  • Alessandro Vespignani

United States Department of Health and Human Services (5U01IP0001137)

  • Matteo Chinazzi
  • Kunpeng Mu
  • Xinyue Xiong
  • Alessandro Vespignani

National Science Foundation (2027007)

  • Ajitesh Srivastava

United States Department of Health and Human Services

  • Shaun Truelove
  • Claire P Smith
  • Justin Lessler
  • Juan Dent Hulse
  • Joshua Kaminsky
  • Elizabeth C Lee
  • Javier Perez-Saez
  • Alison Hill

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Talía Malagón, McGill University, Canada

Version history

  1. Preprint posted: August 31, 2021 (view preprint)
  2. Received: September 2, 2021
  3. Accepted: June 3, 2022
  4. Accepted Manuscript published: June 21, 2022 (version 1)
  5. Version of Record published: June 24, 2022 (version 2)

Copyright

This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.

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  1. Shaun Truelove
  2. Claire P Smith
  3. Michelle Qin
  4. Luke C Mullany
  5. Rebecca K Borchering
  6. Justin Lessler
  7. Katriona Shea
  8. Emily Howerton
  9. Lucie Contamin
  10. John Levander
  11. Jessica Salerno
  12. Harry Hochheiser
  13. Matt Kinsey
  14. Kate Tallaksen
  15. Shelby Wilson
  16. Lauren Shin
  17. Kaitlin Rainwater-Lovett
  18. Joseph C Lemairtre
  19. Juan Dent Hulse
  20. Joshua Kaminsky
  21. Elizabeth C Lee
  22. Javier Perez-Saez
  23. Alison Hill
  24. Dean Karlen
  25. Matteo Chinazzi
  26. Jessica T Davis
  27. Kunpeng Mu
  28. Xinyue Xiong
  29. Ana Pastore y Piontti
  30. Alessandro Vespignani
  31. Ajitesh Srivastava
  32. Przemyslaw Porebski
  33. Srinivasan Venkatramanan
  34. Aniruddha Adiga
  35. Bryan Lewis
  36. Brian Klahn
  37. Joseph Outten
  38. Mark Orr
  39. Galen Harrison
  40. Benjamin Hurt
  41. Jiangzhuo Chen
  42. Anil Vullikanti
  43. Madhav Marathe
  44. Stefan Hoops
  45. Parantapa Bhattacharya
  46. Dustin Machi
  47. Shi Chen
  48. Rajib Paul
  49. Daniel Janies
  50. Jean-Claude Thill
  51. Marta Galanti
  52. Teresa K Yamana
  53. Sen Pei
  54. Jeffrey L Shaman
  55. Jessica M Healy
  56. Rachel B Slayton
  57. Matthew Biggerstaff
  58. Michael A Johansson
  59. Michael C Runge
  60. Cecile Viboud
(2022)
Projected resurgence of COVID-19 in the United States in July-December 2021 resulting from the increased transmissibility of the Delta variant and faltering vaccination
eLife 11:e73584.
https://doi.org/10.7554/eLife.73584

Share this article

https://doi.org/10.7554/eLife.73584

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    Non-pharmaceutical interventions implemented to block SARS-CoV-2 transmission in early 2020 led to global reductions in the incidence of invasive pneumococcal disease (IPD). By contrast, most European countries reported an increase in antibiotic resistance among invasive Streptococcus pneumoniae isolates from 2019 to 2020, while an increasing number of studies reported stable pneumococcal carriage prevalence over the same period. To disentangle the impacts of the COVID-19 pandemic on pneumococcal epidemiology in the community setting, we propose a mathematical model formalizing simultaneous transmission of SARS-CoV-2 and antibiotic-sensitive and -resistant strains of S. pneumoniae. To test hypotheses underlying these trends five mechanisms were built into the model and examined: (1) a population-wide reduction of antibiotic prescriptions in the community, (2) lockdown effect on pneumococcal transmission, (3) a reduced risk of developing an IPD due to the absence of common respiratory viruses, (4) community azithromycin use in COVID-19 infected individuals, (5) and a longer carriage duration of antibiotic-resistant pneumococcal strains. Among 31 possible pandemic scenarios involving mechanisms individually or in combination, model simulations surprisingly identified only two scenarios that reproduced the reported trends in the general population. They included factors (1), (3), and (4). These scenarios replicated a nearly 50% reduction in annual IPD, and an increase in antibiotic resistance from 20% to 22%, all while maintaining a relatively stable pneumococcal carriage. Exploring further, higher SARS-CoV-2 R0 values and synergistic within-host virus-bacteria interaction mechanisms could have additionally contributed to the observed antibiotic resistance increase. Our work demonstrates the utility of the mathematical modeling approach in unraveling the complex effects of the COVID-19 pandemic responses on AMR dynamics.

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    The aim of our study was to test the hypothesis that the community contact tracing strategy of testing contacts in households immediately instead of at the end of quarantine had an impact on the transmission of SARS-CoV-2 in schools in Reggio Emilia Province.

    Methods:

    We analysed surveillance data on notification of COVID-19 cases in schools between 1 September 2020 and 4 April 2021. We have applied a mediation analysis that allows for interaction between the intervention (before/after period) and the mediator.

    Results:

    Median tracing delay decreased from 7 to 3.1 days and the percentage of the known infection source increased from 34–54.8% (incident rate ratio-IRR 1.61 1.40–1.86). Implementation of prompt contact tracing was associated with a 10% decrease in the number of secondary cases (excess relative risk –0.1 95% CI –0.35–0.15). Knowing the source of infection of the index case led to a decrease in secondary transmission (IRR 0.75 95% CI 0.63–0.91) while the decrease in tracing delay was associated with decreased risk of secondary cases (1/IRR 0.97 95% CI 0.94–1.01 per one day of delay). The direct effect of the intervention accounted for the 29% decrease in the number of secondary cases (excess relative risk –0.29 95%–0.61 to 0.03).

    Conclusions:

    Prompt contact testing in the community reduces the time of contact tracing and increases the ability to identify the source of infection in school outbreaks. Although there are strong reasons for thinking it is a causal link, observed differences can be also due to differences in the force of infection and to other control measures put in place.

    Funding:

    This project was carried out with the technical and financial support of the Italian Ministry of Health – CCM 2020 and Ricerca Corrente Annual Program 2023.