Two studies have found that the federal government’s stay-at-home orders have had a greater impact on slowing down the spread of COVID-19, the infection caused by the novel coronavirus.

One study, published in the Journal of the American Medical Association (JAMA), found a significant difference in the number of coronavirus cases between border regions in Illinois, which follows stay-at-home orders, and Iowa, which does not.

Another study, published in Health Affairs, analyzed and measured the degree to which shelter-in-place order has decreased the spread of COVID-19, compared with other social distancing measures.

The JAMA study compared daily changes in coronavirus cases in seven counties bordering Illinois and eight counties bordering Iowa before and after March 21, when Illinois issues stay-at-home orders. Iowa is among the five states that do not have stay-at-home orders.

Before the Illinois order, the number of cases was similar in the border counties. However, after the order was issued, the number of cases increased quickly in Iowa and slowly in Illinois.

Study author George Wehby told Medscape Medical News, “This is the upper bound of the potential difference in cases had a stay-in-home order been in place in Iowa.” He cautioned that there was “a lot of uncertainty in the evidence. Other factors could have come into play.”

Wehby noted that this “is not a causal study. It’s a descriptive study examining how these two areas compared when they started pretty similarly, and one of them had an early stay-at-home order that also closed essential businesses. It’s an association suggesting there is a possible link and effect, but I wouldn’t say this is a direct result of the stay-at-home order.”

The Health Affairs study looked at the relative impact of social distancing measures that state and local governments started following in March and April to contain the spread of the virus. The measures included bans on mass events, closures of schools, gyms, bars, entertainment venues, and restaurant dining areas, and shelter-in-place orders.

The researchers analyzed the impact of these social distancing measures on COVID-19 case growth from March 1 to April 27.

The authors wrote, “Adoption of government-imposed social distancing measures reduced the daily growth rate by 5.4 percentage points after 1–5 days, 6.8 after 6–10 days, 8.2 after 11–15 days, and 9.1 after 16–20 days.”

“Holding the amount of voluntary social distancing constant, these results imply 10 times greater spread [than the actual number of cases] by April 27 without SIPOs (10 million cases) and more than 35 times greater spread without any of the four measures (35 million),” they concluded. They explained that there was no significant impact on lowering the number of cases after the ban on large events or school closures. However, closure of gyms, restaurants, bars, and entertainment centers did have a statistically significant reduction in the spread of COVID-19. Also, shelter-in-place orders led to a significant reduction in the growth of COVID-19 cases.