Summary: Preliminary findings from a new model indicate that strong COVID-19 restrictions should remain in place for more than six weeks. The analysis shows it typically takes nearly three weeks to reach a moderation phase (growth rate below 10% and doubling time over seven days), about one month to reach control (growth rate around 1%), and roughly 45 days to reach containment.
Source: UCR
How long must COVID-19 restrictions last?
A study analyzing 36 countries and all 50 U.S. states concludes that aggressive measures to slow COVID-19 need to be maintained for at least 44–45 days to achieve containment. The research is co-authored by Professor Gerard Tellis (USC Marshall School of Business), Professor Ashish Sood (UC Riverside’s A. Gary Anderson Graduate School of Management), and Nitish Sood (Augusta University). The paper, titled “How Long Must Social Distancing Last,” is published on SSRN.
The authors use two straightforward, generalizable metrics to track the epidemic: daily growth rate and doubling time. The daily growth rate measures the percentage increase in cumulative cases from one day to the next. Doubling time is the number of days it would take for total reported cases to double at the current growth rate. These measures are less susceptible to cross-country reporting differences than absolute case counts.
Professor Tellis noted, “Counts of total or new cases can be misleading and difficult to compare across countries. Growth rate and time to double are critical metrics for understanding how the disease is spreading.”
The researchers establish three practical benchmarks that public health officials can use to set targets and assess progress:
- Moderation: growth rate stays below 10% and doubling time exceeds seven days;
- Control: growth rate stays below 1% and doubling time exceeds 70 days;
- Containment: growth rate falls to about 0.1% and doubling time exceeds 700 days.
Using these benchmarks, the study finds that once strict interventions are implemented, many large countries take roughly three weeks to reach moderation, about four weeks to reach control, and approximately 45 days to achieve containment. When interventions are less aggressive or delayed, achieving these benchmarks can take substantially longer. The authors emphasize that larger countries tend to require more time to reach moderation than smaller countries.
The study defines aggressive intervention to include lockdowns, stay-at-home orders, mass testing, and effective quarantine measures. The researchers point out that examples like Singapore and South Korea—where massive testing and targeted quarantine were deployed—offer a successful alternative to widespread lockdowns and stay-at-home mandates.
The authors draw on methods commonly used to study diffusion of innovations and new technologies. They apply those same concepts and tools to model the diffusion of the virus and the impact of interventions designed to slow its spread. The parallels allow the researchers to propose clear, time-based expectations for policymakers and health administrators.
Professor Sood commented, “Even though there are large differences among countries, it is striking how many similar patterns emerge after aggressive intervention—first moderation, then control, and finally containment.” Professor Tellis added that factors such as country size, border policies, cultural greeting behaviors (bowing versus handshakes or kisses), and environmental conditions like temperature and humidity may help explain observed differences in timing and spread.
The analysis strengthens the argument for early, decisive action. Whether through strict lockdowns as seen in parts of Europe and the United States, or through extensive testing and quarantine as in parts of Asia, aggressive measures are the common factor in nations that move more quickly toward containment. However, the U.S. faces a particular challenge: implementation of aggressive measures has varied widely across states. Because only about half of U.S. states adopted aggressive interventions promptly, states that achieve control or containment may still be vulnerable to imported infections from states that acted later.
Source:
UCR
Media Contact:
Imran Ghori – UCR
Image Source:
The image is in the public domain.
Original Research:
“How Long Should Social Distancing Last? Predicting Time to Moderation, Control, and Containment of COVID-19” by Ashish Sood et al., SSRN. DOI: 10.2139/ssrn.3562996.
Abstract (summary)
The paper addresses the urgent public question of how long social distancing and similar restrictions must continue by proposing two robust metrics—daily growth rate and time to double cumulative cases—and three actionable benchmarks: moderation (growth <10%), control (growth <1%), and containment (growth ≈0.1%). An analysis of the top 36 affected countries and all 50 U.S. states through the end of March finds that any observed slowdown has been driven by aggressive interventions. On average, countries implemented action within about three weeks; after intervention, moderation follows in roughly three weeks, control in about four weeks, and containment in just over six weeks. Without a vaccine, a cure, or widespread testing and quarantine, lockdowns and stay-at-home orders may need to be sustained for months. In federations like the U.S., inconsistent timing and adoption of interventions across regions increase the risk that areas achieving control could be re-exposed by regions that acted later.