Illinois imposed a swift lockdown, while Iowa never ordered residents to stay home. A comparison of bordering counties reveals the price Iowa paid.

• A new study compares coronavirus cases in Iowa, which never imposed a stay-at-home order, to cases in Illinois, where officials implemented a swift lockdown.
• The researchers concluded that a stay-at-home order might have prevented around 30% of cases in Iowa's border counties from March 21 to April 20.
• Illinois's lockdown, meanwhile, likely helped limit infections in the state.

Iowa is one of the five US states that never imposed a statewide stay-at-home order. A new study suggests it probably should have.

The research compares daily coronavirus cases across eight counties in Iowa to the numbers in seven counties in Illinois, where officials swiftly issued a lockdown. The counties all sit along the border between the two states.

The findings, published in the Journal of the American Medical Association, show that cases continued to climb in both states following the Illinois stay-at-home order, but rose more quickly in the Iowa counties. The researchers concluded that the lockdown may have helped limit infections in Illinois — and that Iowa could have benefited from the same policy.

An estimated 30% of cases in Iowa border counties could have been prevented by a stay-at-home order, the researchers calculated.

Iowa counties reported more daily infections

Border comparisons are one of the best ways to determine the effects of a policy change, since neighboring counties tend to share many of the same demographic and socioeconomic characteristics.

Illinois's stay-at-home order went into place at 5 p.m. on March 21, though the state had already shut down bars and restaurants on March 15 and closed schools two days after that. Prior to the statewide shutdown, border counties in Iowa and Illinois had about the same number of coronavirus cases relative to their population sizes: less than one daily case per 10,000 residents.

Illinois's order included a directive to prohibit gatherings larger than 10 people and close all playgrounds, state parks, and nonessential businesses.

Iowa, by contrast, never ordered residents to stay home and was slower to roll out other restrictive measures. The state banned large gatherings and closed bars and restaurants on March 17. Nine days later, it closed some nonessential businesses like dental offices, barbershops, and clothing stores. Iowa recommended that all primary and secondary schools close on March 15, but didn't officially impose the restriction until April 2. By April 6, some additional businesses like malls, museums, and libraries closed as well.

Gov. Kim Reynolds said these measures were essentially "equivalent" to Illinois's stay-at-home order.

"A lot of the things that we've already implemented are included in the shelter-in-place orders that states are putting in place," Reynolds said at a news conference on March 25. "What's the benefit from taking that additional step?"

But the new study found that one month after the Illinois lockdown, border counties in that state were reporting around 10 daily cases per 10,000 residents. Iowa counties, meanwhile, were reporting more than 15 daily cases per 10,000 residents. The researchers determined that Iowa counties saw an excess of 217 infections during that time period.

One complicating factor in this data, however, is the fact that Illinois ramped up coronavirus testing following its stay-at-home order. Before March 21, both Iowa and Illinois were testing at about the same rate (less than 20 tests per 10,000 residents). By April 20, Illinois was conducting 117 tests per 10,000 residents compared to 82 tests per 10,000 residents in Iowa. The more a state tests, the more likely it is to identify infections.

But the researchers determined that Iowa's slower testing rate likely did not influence their study's results (unless county-level testing rates were dramatically different from those at the state level).

Stay-at-home measures come at a price

Similar research has determined that lockdowns helped reduce coronavirus transmission in China and Italy. An April working paper also found that California's shelter-in-place order (the first in the US) resulted in nearly 50,000 fewer infections and prevented more than 1,600 deaths from March 19 to April 20.

"Social distancing provided by the lockdowns has clearly slowed the spread of the virus," Jeffrey Morris, director of the biostatistics division at the University of Pennsylvania, recently told Business Insider. But he added that total lockdowns — including school shutdowns, non-essential business closures, and stay-at-home orders — "tend to be an overreach from what is necessary to confer protection."

Indeed, the study of California's outbreak found that reducing COVID-19 cases there came at a painful cost: For every life saved during that month, around 400 people lost their jobs.