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As COVID-19 cases surge, more state officials are implementing lockdowns. VALERIE MACON/Getty Images
  • Restrictions are often based on a mix of data that shows a dangerous trend of rising infections in a community.
  • Data that indicates a healthcare system is becoming overwhelmed may lead to cancellations of nonessential procedures.
  • Experts say lockdown rules need to be practical and easy to follow in order to get the public to comply.

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The latest surge of COVID-19 is spurring new restrictions across the country.

In the last few weeks, California imposed regional stay-at-home orders, New York City closed and reopened public schools, Massachusetts announced it would roll back to an earlier phase of reopening, and Mississippi capped indoor gatherings to no more than 10 people.

While each state has different approaches to restrictions, most share one thing in common: the use of key health metrics to decide when to reopen — and when to shut down.

Here’s a look at the data public health experts use to advise officials on lockdowns.

A rise in COVID-19 cases in a particular area may trigger lockdowns.

There are different numbers officials can use to track cases, such as data on test positivity rates and the number of people who show up at a medical facility with symptoms of COVID-19.

Even though this data is often updated daily, officials usually look at it over a 7- or 14-day period to get a sense of the direction infections are going.

“If I see a big spike one day, it doesn’t really mean much, but seeing that same spike over several days matters,” said Brian Labus, PhD, MPH, assistant professor of epidemiology and biostatistics at the University of Nevada, Las Vegas’ School of Public Health and a member of Nevada Gov. Steve Sisolak’s task force to advise on the scientific aspects of the COVID-19 pandemic.

An upward trend may drive an official to introduce new restrictions to help stop the spread in particularly risky situations, such as nightlife and social gatherings.

The exact threshold on infection trends that trigger a lockdown can vary by location.

Sometimes officials don’t have specific numbers they’re looking for when closing down businesses and services, said Susan Hassig, DrPH, MPH, associate professor of epidemiology at Tulane University’s School of Public Health and Tropical Medicine.

“That’s what’s really challenging about having a shared conversation about metrics and triggers for certain things happening,” she said.

“Entities like governors and mayors have had much better clarification for when to reopen, but far less concrete benchmarks for closing back down again, and that’s problematic in terms of people not knowing what to expect,” Hassig said.

Another important factor in determining lockdowns is how hospitals are doing.

Public health officials want to ensure that hospitals have enough bandwidth to treat people with COVID-19 and other medical emergencies, like a heart attack or injuries from a car accident.

The percentage of occupied beds compared with available beds in the intensive care unit is a common data point that can indicate how overwhelmed the healthcare system is in a given state, region, or city.

Officials at the hospitals and governments may also track the rate of hospitalizations and whether it’s trending up or down. They may also track the availability of healthcare workers and the ability for hospitals to increase their capacity.

If data points to a situation in which hospitals may soon become overwhelmed, healthcare facilities may stop offering some procedures to preserve their capacity, Labus said.

“They call them nonessential surgeries because people won’t die if they don’t get them, but it does affect people’s quality of life,” he said. “If you’re trying to plan ahead, say you need a new hip or something, you may need to put it off, and that’s where people will really see it.”

Data on new hospital admissions can also be used as a tool to understand a rise in severe cases in a community, and whether additional restrictions and business closures need to be implemented to reduce the spread of the virus.

Discouraging data on hospitals and trends can form the basis of lockdowns. But the ways in which officials restrict businesses and lifestyle activities can vary quite a bit from location to location.

“The objective of any decision-maker is going to greatly guide what restrictions they ultimately put in place, and how they go about approaching that,” Hassig said. “The question is: When does it get bad enough to do something about it?”

Officials are often trying to strike a balance between competing interests, such as reducing the spread of the virus, and making sure businesses and schools can stay open.

They also need to take into account the likelihood at which restrictions will be followed.

“If I know 95 percent of the public is not going to follow a mandate, it doesn’t make sense to put that in,” Labus said. “If I ask people to reduce their travel or shopping for a few days, that may be a more realistic thing. It has to be practical.”

This results in lockdown rules that can feel somewhat arbitrary to everyday people.

They wonder why, for example, sit-down dining capacity is cut to 25 percent, instead of 30 or 20 percent, or why 10 was chosen as the maximum number of attendees for an indoor gathering.

“It’s not like we have a formula where you can plug in numbers, and it says restaurant capacity should be cut by a certain percent,” said Labus, adding that officials try to create restrictions that are easy to understand and follow.

“No one’s expecting it to be perfect,” he said. “Even if people are not following restrictions completely, the rules still cut down on the number of people gathering and reduce the risk of transmission.”

And as for figuring out whether lockdowns are effective, people should expect a lag time of at least a few weeks.

“To figure out restrictions, we’re looking at data from what happened a couple of weeks ago and trying to make decisions right now,” Labus said. “I will not see the effect of shutdowns and masking requirements for about 3 weeks.”