SARS-CoV-2 Transmission Potential and Policy Changes in South Carolina, February 2020 – January 2021

Abstract

Introduction: We aimed to examine how public health policies influenced the dynamics of COVID-19 time-varying reproductive number (R t ) in South Carolina from February 26, 2020 to January 1, 2021. Methods: COVID-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 R t using EpiEstim. We performed linear regression to evaluate if per-capita cumulative case count varies across counties with different population size. Results: R t shifted from 2-3 in March to <1 during April and May. R t rose over the summer and stayed between 1.4 and 0.7. The introduction of statewide mask mandates was associated with a decline in R t (-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). Conclusion: The R t 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 R t reduction, while policies that encouraged more movement, such as re-opening schools, were associated with R t increase.

Effectiveness of social distancing measures and lockdowns for reducing transmission of COVID-19 in non-healthcare, community-based settings

“…Nine showed an increasing trend in the number of daily new confirmed COVID-19 cases, growth rate or Rt of COVID-19. One study in South Carolina, US, estimated the Rt increased by 12.3% (95% CrI: 10.1%, 14.4%) after schools reopened at the end of August 2020 [ 21 ]. However, one study found that the reopening of schools did not immediately impact SARS-CoV-2 incidence, and an increase in incidence was not observed until 13 weeks after reopening [ 203 ].…”

“…These were carried out at a national and sub-national scale, with nine studies conducted within the first year of the pandemic (electronic supplementary material, appendix C). Ten studies examined the effectiveness of workplace measures using population-level data [ 17 , 21 , 55 , 234 , 236 – 238 , 240 – 243 ]. Six studies assessed workplace mobility to explain the variation in the COVID-19 growth rate, case numbers or Rt [ 17 , 55 , 234 , 236 , 237 , 240 ] consistently showed that reduced workplace mobility was significantly associated with reduced SARS-CoV-2 incidence or transmission [ 234 , 236 , 237 , 240 ].…”

“…Twelve studies examined the impact of reopening schools [21,[201][202][203][204][205][206][207][208][209][210][211]. Nine showed an increasing trend in the number of daily new confirmed COVID-19 cases, growth rate or Rt of COVID-19.…”

“…Twelve observational studies were included in the review for workplace measures [17,21,41,55,[233][234][235][236][237][238][239][240]. These were carried out at a national and sub-national scale, with nine studies conducted within the first year of the pandemic (electronic supplementary material, appendix C).…”