Causal impact of spontaneous relaxation of social distancing practices on spread of SARS-CoV-2 in US

The highly contagious novel coronavirus caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), which emerged in December 2019 in Wuhan, China, rapidly transformed into a pandemic.

Study: Social Distancing Causally Impacts The Spread of SARS-CoV-2: A U.S. Nationwide Event Study. Image Credit: oatawa/ShutterstockStudy: Social Distancing Causally Impacts The Spread of SARS-CoV-2: A U.S. Nationwide Event Study. Image Credit: oatawa/Shutterstock

SARS-CoV-2 infection has been associated with significant morbidity and mortality, and the virus can be transmitted through person-to-person contact, respiratory droplets in aerosols, as well as fomites. Since contaminated respiratory droplets can travel a minimum distance of six feet, many countries mandated social distancing measures, beginning the first wave of the pandemic.

In the United States (US), the extent and type of social distancing policies adopted differ across states. After the state-imposed restrictions towards social distancing, a reduction in the number of cases were noted across the counties. However, evidence from another research indicates that such measures merely stabilize the spread of SARS-CoV-2 but do not aid in reducing the daily growth rate of COVID-19. Despite the clear association between the infection rate and implementation of social distancing, the causal impact of social distancing on the spread of SARS-Cov-2 remains obscure.

The study

The purpose of a recent study available of In Review* was to examine the causal impact of a spontaneous relaxation of social distancing measures on the spread of SARS-CoV-2.

This experimental study was initiated during the abrupt relaxation of social distancing practices due to the nationwide mass protests after George Floyd’s tragic death on May 25, 2020. Here, the direct effect of social distancing was analyzed by utilizing the increase in the population’s mobility during the protest period.

For this purpose, publicly accessible data – from the John Hopkins GitHub repository was referred to and the statistical methods complied with relevant guidelines and regulations. The number of new cases for each county on each day was calculated by subtracting the cumulative number of confirmed cases at the end of the day from the number of cumulative cases from the previous day. The data-set comprised 474,422 county-days representing 3,142 counties from all fifty states and the District of Columbia (DC) from January-June 2020.

Results

It was noted that over the entire sample period, the SARS-CoV-2 infection rate was 1.22 cases per day higher, per 100,000 population, in the counties where protests took place relative to the counties with no protests.

The coefficient associated with PostGF (after George Floyd’s death) was positive and highly significant. The findings revealed that the SARS-CoV-2 infection rate increased by 3.39 cases per day, per 100,000 population, across the US following the onset of the protests. The infection rate was greater in the counties in which protests took place following the onset of the protests. Therefore, the impact of relaxation of social distancing practices on the spread of SARS-CoV-2 was evident.

In fact, in the period preceding the onset of the protests, the number of new coronavirus disease 2019 (COVID-19) cases was steadily declining across the country. Thereafter, several states were strategically phasing out their social distancing policies. At this juncture, social mobility (wherein individuals can be mobile while still maintaining the required minimum six feet distances amongst each other) was on the rise. The concurrent relaxations of the measures during the event period may have tempted the people to let go of their social distancing practices. It was noted that even relaxation of so

Consequently, the deductions showed that social distancing restrictions and social mobility are correlated with one another. Social mobility is projected to rise when travel restrictions are lifted. After controlling for the reduction in social distancing restrictions and increased social mobility during the protests, a significant increase in the number of daily COVID-19 cases was noted across all counties. This increase was higher in counties where the protests took place. The mass protests gathered people in close physical proximity to one another.

Additionally, a placebo test was carried out, assessing the causal impact of the protests on the spread of SARS-CoV-2. A Monte Carlo simulation exercise was implemented for this purpose. The results prompted the rejection of the null hypothesis that the causal impact of protests on the SARS-CoV-2 infection rate could be due to pure chance.

The results documented a country-wide increase in SARS-CoV-2 infection rate of more than 3.06 cases per day, per 100,000 population, following the onset of the protests, and a further increase of 1.73 cases per day, per 100,000 population, in regions where the protests took place.

The data represented a 61.2% country-wide increase in COVID-19 cases, compared to the average number of new COVID-19 cases per day during the week preceding the onset of the protests. Furthermore, a 34.6% increase was documented in the protest counties.

Conclusion

The findings confirmed that social distancing practices causally impact the spread of SARS-CoV-2; thus, relaxation of social distancing restrictions has important public health implications. Hence, policymakers should be informed about the use of social distancing as an intervention in minimizing the spread of SARS-CoV-2. Such measures can aid in preventing the spread of SARS-CoV-2 and may reduce the probability of occurrence of upcoming waves of COVID-19.

*Important notice

This study is a preliminary scientific report that has not yet been peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Nidhi Saha

Written by

Nidhi Saha

I am a medical content writer and editor. My interests lie in public health awareness and medical communication. I have worked as a clinical dentist and as a consultant research writer in an Indian medical publishing house. It is my constant endeavor is to update knowledge on newer treatment modalities relating to various medical fields. I have also aided in proofreading and publication of manuscripts in accredited medical journals. I like to sketch, read and listen to music in my leisure time.

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