How is everyone faring this lovely quarantine? All good? I have some good news and some bad news. The good part is that quarantines work for slowing down the spread of viruses and if we all keep up the good work, it will come to an end. The bad part is that we may have to keep at it for at least six weeks in total, according to a new study.

The paper looked at 36 countries and 50 U.S. states and reports that aggressive intervention to contain COVID-19 (read: mass quarantine) must be maintained for at least 44 days for optimal results.

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“Counts of total or new cases can be misleading and difficult to compare across countries,” said Professor Gerard Tellis of USC Marshall School of Business, one of the study’s co-authors. “Growth rate and Time to double are critical metrics for an accurate understanding of how this disease is spreading.”

The authors used the daily growth rate of the virus and time-to-double for cumulative cases in order to study its transmission patterns in society. These two metrics are reliable and generally applicable to any other pathogen, they explain. Daily growth represents the increase in cases on a day by day basis (in percentages), while time-to-double represents the length of time a pathogen needs to double its number of infections.

By looking at these two metrics, the team established three benchmarks to serve as targets for healthcare specialists:

• 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.
• Containment: when growth rate remains 0.1% and doubling time stays above 700 days.

The team’s preliminary results suggest that large countries take around three weeks to see a moderation of the infection, one month to get to the control phase, and 45 days to achieve containment, once aggressive intervention measures are in place. If less aggressive intervention methods are implemented, however, this process can take significantly longer, the team explains. They defined aggressive intervention as lockdowns, stay-at-home orders, mass testing, and quarantines.

A country’s size also factors in — larger countries, the authors note, take longer to reach the moderation phase than smaller ones.

“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,” says co-author Nitish Sood, a student at Augusta University studying Cellular & Molecular Biology.

“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.”

Other local factors such as the layout and security of borders, cultural customs around greetings (for example bowing versus handshaking and kissing), temperature, humidity, and geographical location explain the differences seen between individual countries.

The results point to the need for adopting aggressive measures against outbreaks no matter the country. The U.S. may have a unique challenge because of its federal constitution, they add, noting that only half of the states have so far implemented such measures, and they’ve all done so at varying times. Even if these states successfully control or contain the virus, they may be exposed from states that didn’t or were late to do so.

The paper “How Long Should Social Distancing Last? Predicting Time to Moderation, Control, and Containment of COVID-19” has been published in the SSRN Electronic Journal.