ABSTRACT
IntroductionWe aimed to examine how public health policies influenced the dynamics of COVID-19 time-varying reproductive number (Rt) in South Carolina from February 26, 2020 to January 1, 2021. MethodsCOVID-19 case series (March 6, 2020 - January 10, 2021) were shifted by 9 days to approximate the infection date. We analyzed the effects of state and county policies on Rt using EpiEstim. We performed linear regression to evaluate if per-capita cumulative case count varies across counties with different population size. ResultsRt shifted from 2-3 in March to <1 during April and May. Rt rose over the summer and stayed between 1.4 and 0.7. The introduction of statewide mask mandates was associated with a decline in Rt (-15.3%; 95% CrI, -13.6%, -16.8%), and school re-opening, an increase by 12.3% (95% CrI, 10.1%, 14.4%). Less densely populated counties had higher attack rate (p<0.0001). ConclusionThe Rt dynamics over time indicated that public health interventions substantially slowed COVID-19 transmission in South Carolina, while their relaxation may have promoted further transmission. Policies encouraging people to stay home, such as closing non-essential businesses, were associated with Rt reduction, while policies that encouraged more movement, such as re-opening schools, were associated with Rt increase.
ABSTRACT
PurposeTo examine the time-varying reproduction number, Rt, for COVID-19 in Arkansas and Kentucky and investigate the impact of policies and preventative measures on the variability in Rt. MethodsArkansas and Kentucky county-level COVID-19 cumulative case count data (March 6-November 7, 2020) were obtained. Rt was estimated using the R package EpiEstim, by county, region (Delta, non-Delta, Appalachian, non-Appalachian), and policy measures. ResultsThe Rt was initially high, falling below 1 in May or June depending on the region, before stabilizing around 1 in the later months. The median Rt for Arkansas and Kentucky at the end of the study were 1.15 (95% credible interval [CrI], 1.13, 1.18) and 1.10 (95% CrI, 1.08, 1.12), respectively, and remained above 1 for the non-Appalachian region. Rt decreased when facial coverings were mandated, changing by -10.64% (95% CrI, -10.60%, -10.70%) in Arkansas and -5.93% (95% CrI, -4.31%, -7.65%) in Kentucky. The trends in Rt estimates were mostly associated with the implementation and relaxation of social distancing measures. ConclusionsArkansas and Kentucky maintained a median Rt above 1 during the entire study period. Changes in Rt estimates allows quantitative estimates of potential impact of policies such as facemask mandate.
ABSTRACT
In 2020, SARS-CoV-2 impacted Georgia, USA. Georgia announced state-wide shelter-in-place on April 2 and partially lifted restrictions on April 27. We analyzed daily incidence of confirmed COVID-19 cases by reporting date, March 2-June 14, in Georgia, Metro Atlanta, and Dougherty County and estimate the time-varying reproduction number, Rt, using R package EpiEstim. The median Rt estimate in Georgia dropped from between 2 and 4 in mid-March, to <2 in late March, and around 1 from mid-April to mid-June. Regarding Metro Atlanta, Rt fluctuated above 1.5 in March and around 1 since April. In Dougherty County, the median Rt declined from around 2 in late March to 0.32 on April 26. In Spring 2020, SARS-CoV-2 transmission in Georgia declined likely because of social distancing measures. However, as restrictions were relaxed in late April, community transmission continued with Rt fluctuating around 1 across Georgia, Metro Atlanta, and Dougherty County as of mid-June.
