People are moving more in Michigan. Here’s what that means for the spread of COVID-19.
Michiganders are getting back on the move.
An analysis of anonymous cell phone mobility data from the Cuebiq Mobility Index shows that movement dropped significantly in the state ahead of Gov. Whitmer’s stay-at-home order that went into effect March 24, and managed to maintain that low level of movement for approximately four weeks.
But the average amount of movement has increased since April 12, despite the stay-at-home order remaining in place.
Check out the graph below to see the amount of movement in Michigan from March 8 to May 10. Each faded gray line represents a county, and the red line shows the state’s average.
Gov. Whitmer has called this increase of movement concerning.
“If this is community spread across the state, like we saw eight weeks ago, it would make it more likely that we have to continue a stay-at-home posture, and that’s the last thing any of us wants," she said. "So everyone needs to keep doing their part.”
But Whitmer added that it’s not the movement itself that’s necessarily a problem, so long as people wear their masks outside, follow social distancing, and wash their hands regularly.
Joseph Eisenberg agrees. He’s a professor of global health at the University of Michigan, and chair of the school’s epidemiology department.
“Just because somebody is moving doesn’t necessarily mean they are in contact with other people," he said. "They could be driving in their own car across the state, from one house to another house, and that’s pretty much zero contact.”
Eisenberg says that’s very different from high-risk settings, such as bars, concerts, or college dorms – settings that carry a high risk of transmission.
Michigan remains under a stay-at-home order until at least May 28. But the governor has started to slowly reopen parts of the economy, including restaurants in the Upper Peninsula and northern Lower Peninsula. Long-distance movement is still a concern, since people traveling from counties with higher case counts could spread the disease to those that have largely avoided major outbreaks.
“Long-distance movement has the risk of introducing pathogens from one area to another, so there’s certainly risks associated with it,” says Eisenberg, “but it’s not necessarily a sign that we’re going to go back to the same level of transmission, as long as we do some of the other things right. And that’s really the goal. The goal is to have us get back to some sense of normalcy, but still control the virus.”
Trading one intervention for another
Michigan has been under a strict stay-at-home order for nearly eight weeks now. The data show that people were largely cooperative in working to “flatten the curve” for about six weeks, including the drop in movement that occurred before the official stay-at-home order. That effort may have limited the spread of COVID-19, which has infected at least 50,000 Michiganders and killed 5,000 in three months.
Joseph Eisenberg says that level of extreme reduction of movement was necessary.
“I think that the need for a stay-at-home order — to do some drastic reduction of movement — was because we intervened late in the course of the epidemic and we were in an exponential increase. So we really did need to do something drastic to really limit a high degree of people's contact with other people.”
Extreme social distancing is very effective: It appears to have flattened the curve so far, although a second spike remains a possibility if restrictions are loosened too quickly. But it is also inefficient as a long-term solution.
Now that the number of new cases in Michigan is slowing, epidemiologists like Eisenberg are looking at contact rates: the number of contacts you might have per day that could result in transmission. He says based on what we know about the novel coronavirus, you would have to decrease contact by little more than half. So, reopening some restaurants at 50% capacity is one example of how officials plan to reopen while keeping contact rates low.
Widespread testing and contact tracing are also necessary to a safe, effective reopening.
“We basically can trade one intervention, which is mass social distancing, to a much more targeting, efficient way of intervening, and that is monitoring people’s symptoms, having available testing, and then contact tracing," says Eisenberg. "So we can isolate those that are contagious to a certain degree, and therefore continue to minimize transmission.”