Researchers at USC and UC Riverside studied 36 countries and 50 U.S. states and concluded that aggressive restrictions to contain COVID-19 are needed and must be maintained for at least 44 days to curtail the pandemic, according to findings released Tuesday.
The study was co-authored by Gerard Tellis, a professor at the USC Marshall School of Business; and Ashish Sood, a professor at UCR’s A. Gary Anderson Graduate School of Management; with Nitish Sood, a student at Augusta University studying cellular and molecular biology.
In their paper — titled “How Long Must Social Distancing Last” and published in the open sources journal SSRN — the authors identify two simple, intuitive and generalizable metrics of the spread of disease: daily growth rate and time to double cumulative cases. Daily growth rate is the percentage increase in cumulative cases; doubling time is the number of days for cumulative cases to double at the current growth rate.
“Counts of total or new cases can be misleading and difficult to compare across countries,” Tellis said. “Growth rate and time to double are critical metrics for an accurate understanding of how this disease is spreading.”
The researchers then defined three measurable benchmarks for analysts and public health managers to target:
— Moderation: when growth rate stays below 10% and doubling time stays above seven days;
— Control: when growth rate stays below 1% and doubling time stays above 70 days; and
— Containment: when growth rate remains 0.1% and doubling time stays above 700 days.
“These simple, intuitive, and universal benchmarks give public health officials clear goals to target in managing this pandemic,” Sood said.
Preliminary results using that model to analyze the data suggest that once aggressive interventions are in place, large countries take almost three weeks to see moderation, one month to get control, and 45 days to achieve containment. With less aggressive intervention, it can take much longer, the authors said.
Important differences exist by size of country, and public health administrators should note larger countries take longer to see moderation, according to the researchers, who defined aggressive intervention as lockdowns, stay-at-home orders, mass testing and quarantines.
“Singapore and South Korea adopted the path of massive test and quarantine, which seems to be the only successful alternative to costly lockdowns and stay-at-home orders,” Nitish Sood said.
UCR’s Sood said: “Even though huge differences exist among countries, it’s striking to see so many similarities from aggressive intervention to moderation, control, and containment of the spread of the disease.”
Tellis added, “Besides size of country, borders, cultural greetings (bowing versus handshaking and kissing), temperature, humidity and latitude may explain these differences.”
The researchers said their analysis bolsters the case for adopting aggressive measures, whether it’s the aggressive lockdowns of Italy or California, massive testing and quarantine of South Korea or Singapore, or a combination of both as seen in China. However, the U.S. may have a unique challenge because of its federal constitution.
Only half of the states have adopted aggressive intervention and that at varying times. Should those states achieve control or containment, they may be vulnerable to contagion from states that were late to do so, the researchers said.
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