Impact of Non-Pharmaceutical Intervention on COVID-19 Transmission Dynamics in California
Faculty Mentor
Isaac Chun-Hai Fung PhD
Location
Russell Union Ballroom
Type of Research
On-going
Session Format
Poster Presentation
College
Jiann-Ping Hsu College of Public Health
Department
Department of Biostatistics, Epidemiology and Environmental Health Science
Abstract
Impact of Non-Pharmaceutical Intervention on COVID-19 Transmission Dynamics in California
Authors
Patra Ezeamii1 MPH, Nenrot GopepMPH, Francis Kengne1 MPH, Jonathan Luyster1 MPH, Isaac Chun-Hai Fung1 PhD Author affiliation
1Department of Biostatistics, Epidemiology and Environmental Health Science, Jiann-Ping Hsu College of Public Health, Georgia Southern University, Statesboro, GA.
Presenting Author: Patra Ezeamii, MPH DrPH Epidemiology Student Department of Biostatistics, Epidemiology, and Environmental Health Sciences Jiann-Ping Hsu College of Public Health (JPHCOPH) Georgia Southern University Email: pe02061@georgiasouthern.edu
Introduction: California provides a large-scale setting to evaluate SARS-CoV-2 transmission dynamics and policy-associated changes in transmission potential. We conducted both statewide and regional analyses to estimate the time-varying effective reproduction number (Rt) across California and its six Public Health Regions from January 2020 through February 2023, and quantified associations between Rt and five major non-pharmaceutical interventions (NPIs) implemented in 2020.
Methods: Daily confirmed case data were obtained from the Johns Hopkins University repository and cleaned with imputation for the negative and zero case counts. Infection dates were adjusted using deconvolution(R package incidental), infection count via a Poisson-distributed multiplier and Rt was estimated using a 7-day sliding window approach in package EpiEstim. Policy impacts were assessed as percentage changes in non-overlapping time-window Rt before and after 5 key policy orders: stay-at-home order, paid sick leave and COVID-19 protection order, Stage 2 reopening, mandatory face mask order, and extension of roadside business and licensing policies. Posterior sampling generated 95% credible intervals. Sensitivity analyses were conducted using alternative serial interval distributions and prior specifications.
Result: Four epidemic waves were observed (winter 2020–2021; summer 2021; winter 2021–2022; mid-2022). Rt fluctuated around the epidemic threshold (Rt≈1), exceeding 1 prior to major surges. The stay-at-home order was associated with Rt reductions of −2% to −6% across regions, and facemask mandates with reductions of −3% to −8%, with the strongest reductions in the Bay Area and the Greater Sierra-Sacramento region. Stage 2 reopening corresponded to increases of +1% to +6%, and extension of roadside business operations to increases of +4% to +10%, particularly in Los Angeles and the Bay Area. Several regional estimates had credible intervals overlapping zero.
Conclusion: These findings demonstrate regional heterogeneity and indicate that NPIs were associated with modest but directionally consistent changes in Rt, supporting region-specific response strategies in future outbreaks.
Keywords: COVID-19; epidemiology; transmission dynamics; policy interventions; reproduction number
Program Description
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Start Date
4-23-2026 10:00 AM
End Date
4-23-2026 12:00 PM
Recommended Citation
Ezeamii, Patra Chisom; Gopep, Nenrot; Luyster, Jonathan; Kengne, Francis; and Fung, Isaac Chun Hai, "Impact of Non-Pharmaceutical Intervention on COVID-19 Transmission Dynamics in California" (2026). GS4 Student Scholars Symposium. 72.
https://digitalcommons.georgiasouthern.edu/research_symposium/2026/2026/72
Impact of Non-Pharmaceutical Intervention on COVID-19 Transmission Dynamics in California
Russell Union Ballroom
Impact of Non-Pharmaceutical Intervention on COVID-19 Transmission Dynamics in California
Authors
Patra Ezeamii1 MPH, Nenrot GopepMPH, Francis Kengne1 MPH, Jonathan Luyster1 MPH, Isaac Chun-Hai Fung1 PhD Author affiliation
1Department of Biostatistics, Epidemiology and Environmental Health Science, Jiann-Ping Hsu College of Public Health, Georgia Southern University, Statesboro, GA.
Presenting Author: Patra Ezeamii, MPH DrPH Epidemiology Student Department of Biostatistics, Epidemiology, and Environmental Health Sciences Jiann-Ping Hsu College of Public Health (JPHCOPH) Georgia Southern University Email: pe02061@georgiasouthern.edu
Introduction: California provides a large-scale setting to evaluate SARS-CoV-2 transmission dynamics and policy-associated changes in transmission potential. We conducted both statewide and regional analyses to estimate the time-varying effective reproduction number (Rt) across California and its six Public Health Regions from January 2020 through February 2023, and quantified associations between Rt and five major non-pharmaceutical interventions (NPIs) implemented in 2020.
Methods: Daily confirmed case data were obtained from the Johns Hopkins University repository and cleaned with imputation for the negative and zero case counts. Infection dates were adjusted using deconvolution(R package incidental), infection count via a Poisson-distributed multiplier and Rt was estimated using a 7-day sliding window approach in package EpiEstim. Policy impacts were assessed as percentage changes in non-overlapping time-window Rt before and after 5 key policy orders: stay-at-home order, paid sick leave and COVID-19 protection order, Stage 2 reopening, mandatory face mask order, and extension of roadside business and licensing policies. Posterior sampling generated 95% credible intervals. Sensitivity analyses were conducted using alternative serial interval distributions and prior specifications.
Result: Four epidemic waves were observed (winter 2020–2021; summer 2021; winter 2021–2022; mid-2022). Rt fluctuated around the epidemic threshold (Rt≈1), exceeding 1 prior to major surges. The stay-at-home order was associated with Rt reductions of −2% to −6% across regions, and facemask mandates with reductions of −3% to −8%, with the strongest reductions in the Bay Area and the Greater Sierra-Sacramento region. Stage 2 reopening corresponded to increases of +1% to +6%, and extension of roadside business operations to increases of +4% to +10%, particularly in Los Angeles and the Bay Area. Several regional estimates had credible intervals overlapping zero.
Conclusion: These findings demonstrate regional heterogeneity and indicate that NPIs were associated with modest but directionally consistent changes in Rt, supporting region-specific response strategies in future outbreaks.
Keywords: COVID-19; epidemiology; transmission dynamics; policy interventions; reproduction number
