A new pre-print study by a team of Harvard researchers concludes that the idea of a single prolonged lockdown — which many are calling for in the U.S. — is not the most effective or sustainable way to curb the coronavirus epidemic. A more viable, long-term approach is to carry out a series of shorter “intermittent” lockdowns triggered by certain medical care capacity thresholds.

A team of researchers from Harvard’s T.H. Chan School of Public Health posted the study, titled “Social distancing strategies for curbing the COVID-19 epidemic,” Tuesday on the medRxive pre-print server. The study, as underscored by ZDNet’s Tiernan Ray, is yet to be peer-reviewed.

The study’s key finding is that multiple, more targeted social distancing measures would be more effective than one prolonged “lockdown.”

That approach, as Ray explains, would balance the “herd immunity” strategy with the social distancing strategy, allowing society at large to build up immunity while occasionally imposing more drastic social distancing measures, like “stay-at-home” orders, to protect the health care system from being overwhelmed when it reaches certain predetermined thresholds.

“The SARS-CoV-2 [the virus that causes COVID-19] pandemic is straining healthcare resources worldwide, prompting social distancing measures to reduce transmission intensity,” reads the abstract of the study, written by Harvard’s Stephen Iissler, Christine Tedijanto, Marc Lipsitch, and Yonatan Grad. “The amount of social distancing needed to curb the SARS-CoV-2 epidemic in the context of seasonally varying transmission remains unclear.”

“Using a mathematical model, we assessed that one-time interventions will be insufficient to maintain COVID-19 prevalence within the critical care capacity of the United States,” the researchers explain. “Seasonal variation in transmission will facilitate epidemic control during the summer months but could lead to an intense resurgence in the autumn.”

The optimal approach, the study concludes, is “intermittent distancing”: “Intermittent distancing measures can maintain control of the epidemic, but without other interventions, these measures may be necessary into 2022. Increasing critical care capacity could reduce the duration of the SARS-CoV-2 epidemic while ensuring that critically ill patients receive appropriate care.”

What determines when distancing measures should be imposed? The researchers advise that the trigger point should be at maximum 37.5 cases per 10,000 adult people in the population.

“That threshold, they estimate, would keep the number of patients needing critical care at 0.89 persons for every 10,000 people in the population, which should be adequate to not overwhelm the health care system,” Ray explains.

“Widespread surveillance will be required to time the distancing measures correctly and avoid overshooting critical care capacity,” the researchers write. The best way to monitor infection rates are blood tests to determine who has contracted the virus and who has already developed immunity to it, they suggest.

The researchers used the classic epidemiological model known as “SEIR,” which takes into account how many people in a community are “susceptible,” “exposed,” “infectious,” and “recovered,” which, Ray notes, is “a statistical technique, and so it’s important to remember that it’s not a guarantee of future trends, it’s a way to model what might happen.”

Read the full study here.

Related: Nobel Laureate: Why Coronavirus Crisis May Be Over Sooner Than Many Think