A widely cited model that estimates the trajectory of the coronavirus pandemic projects that Tennessee could consider easing social distancing orders soon - but not for about a month - and only if other strong containment measures, such as widespread testing and contact tracing, are in place.
The same model at one point projected potential deaths in Tennessee could be as high as 3,400 through Aug. 4, but that number fell to 587 after the state instituted a stay-at-home policy in early April.
Experts who made those projections say it's too soon to say whether the more dire projections will come roaring back now that Tennessee and Georgia are at the vanguard of several states lifting their stay-at-home orders.
"We don't really know that much about COVID-19, so nobody can pretend in a model that they know the trajectory in every location through some assumptions," said Dr. Christopher Murray, director of the Institute for Health Metrics and Evaluation, an independent global health research center at the University of Washington. "That's why we have, like the National Weather Service has for weather forecasting, a very data-driven approach."
New estimates released Tuesday from the Institute for Health Metrics and Evaluation suggest that 30 states - including Tennessee and Alabama - could reach the threshold where it's safe to relax social distancing mandates around May 20. But Georgia should wait until June 19, according to the report.
The estimates are based on current regulations and don't account for recent announcements by Georgia Gov. Brian Kemp, who plans to reopen parts of the economy on Friday, and Tennessee Gov. Bill Lee, who will let the state's current shelter-in-place order expire on April 30.
Murray said during a news briefing on Friday that as states begin to scale back regulations, the group will revise forecasts and try to capture the timing of reduced mandates and their impact on the spread of disease. However, making predictions on the possible resurgence of the epidemic is premature.
"We want to model based on data that we've observed and not theoretical transmission models, and we've yet to see the experiments - they're starting in Spain - where some relaxation of social distancing after a major epidemic is occurring. That's going to tell us a lot."
Melissa McPheeters, a health policy research professor and co-director of the Center for Improving the Public's Health through Informatics at Vanderbilt University Medical Center, said in an email, "The specific degree to which social distancing affects transmission is an area where there's a great deal of research right now.
(READ MORE: Here's where you can find free COVID-19 drive-thru testing this weekend in Tennessee)
"What we do know is that social distancing is effective at reducing transmission, so it would seem reasonable that as social distancing is lifted, transmission will increase to some degree. We just don't know to what degree," McPheeters said.
Murray said the idea that it would be unwise to relax social distancing in Tennessee before May 20 and in Georgia before June 19 was based on forecasting when the infection rate would be low enough that testing and contact tracing would be manageable.
States with later dates, such as Georgia, were characterized by slowly rising epidemics in places where social distancing hasn't been as strong, he said.
Murray also anticipates those dates will change based on what each state's "peak" looks like. Some states will experience a sharp peak in cases followed by a sharp decline, while other peaks look more like a plateau followed by a steady decline in cases. For example, in Italy and Spain, peak deaths extended over a number of days.
"That will make a difference to when it will be safe to consider relaxing social distancing," Murray said.
Other factors include if adjacent states have many more cases, increasing the risk of importing the disease, and if states are ramping up their testing, contact tracing and case-management capacity to isolate infected individuals - which are essential to containing the virus until a treatment or vaccine becomes available.
"Greater capacity means that it might be reasonable to relax sooner and handle a bigger case load in the community," Murray said.
Experts caution that all models are estimates, and leaders should look to a number of models to inform their decisions.
"Limitations of modeling [are] that, in many respects, it's the best 'guess' and using computational methods to run predictions inputting a number of assumptions," Greg Heath, a public health professor and epidemiologist at the University of Tennessee at Chattanooga, wrote in an email.
For example, Vanderbilt uses a model predicated on person-to-person spread of the virus, but that model does not exactly estimate the transmissibility of the virus, because it does not take into account environmental transmission, Heath said. On the other hand, the Institute for Health Metrics and Evaluation uses the "curve-fitting model" - which must be continually updated, as do all models, as we learn more about the virus itself and the transmission dynamics, he said.
"Identification of those infected is still most important, and having an active COVID-19 surveillance system in place going forward," Heath said. "The public health interventions of social distancing, personal and environmental hygiene, along with case finding, contact tracing, and quarantine all need to be in place prior to scaling back the more rigorous isolation measures."
On Monday, Dr. Aaron Milstone, a pulmonologist treating coronavirus patients and organizer of the 9,500 health care workers who petitioned Tennessee governor for a stay-at-home order, issued a statement in response to Lee's announcement to relax social distancing measures on April 30:
"Rolling back health protections like the stay at home order without first the ability to quickly identify new cases, break chains of transmission, and protect first responders and health care workers from infection only jeopardizes lives and the economy and it goes against the very recommendations of the Centers for Disease Control," Milstone said.
"Covid-19 can spread asymptotically, showing no symptoms, for weeks and is highly more contagious than the typical flu and there is no cure or vaccine. Do you want to be the employer responsible for employees or patrons getting sick or ... dying?"
Contact Elizabeth Fite at efite@timesfreepress.com or 423-757-6673.