NASHVILLE — Up to 50,000 Tennesseans could be hospitalized for COVID-19 under a worst-case scenario model presented last week by Vanderbilt University's Department of Health.
The scenario is one of three offered up by Vanderbilt researchers to show the potential impacts associated with efforts to contain the virus, such as social distancing and widespread testing, as well as efforts to prevent further damage to the economy by doing away with orders to shelter at home.
Researchers said the most dire scenario, in which Tennessee hospitals would be overwhelmed by the outbreak's peak in mid-May with 50,000 sick people requiring hospitalization, would likely only occur if Gov. Bill Lee's current stay-at-home executive order, scheduled to expire April 14, is not renewed. The scenario also assumes that widespread testing, followed by contact tracing of people with known infections, is ended.
Under the scenario, 13% of the population would end up testing positive for COVID-19.
The Vanderbilt model does not project numbers of deaths. The researchers said that's due to factors including some COVID-19 cases are likely going unreported, many initial cases involving younger people and the health of Tennesseans generally ranking low with other states.
The most optimistic scenario, which assumes the COVID-19's rate of infection continues to slow through social distancing and aggressive testing, predicts 2,000 to 3,000 hospitalizations at the outbreak's peak in mid-May.
A third scenario falls in between. It projects what happens should the state's current estimated rate of infection not be flattened further and continues on its current course. Vanderbilt's modeling shows the average infected person right now passes the potentially deadly disease to 1.4 other people.
To flatten the curve, that average needs to fall below 1.0.
Vanderbilt University COVID-19 model’s 3 Tennessee scenarios:
— Optimistic scenario: Assumes gains from social distancing continue to grow through April and May with rate of each person passing along virus to others falling from current 1.5 persons falls to below one. Hospitalizations in mid-May reaches 2,000 to 3,000 which Tennessee hospitals can accommodate.
— Status quo scenario: Assumes state maintains current rate of disease spread through May. Projects mid-June peak with up to 5,000 hospitalization which could “stress” state hospital system.
— Lifting social distancing scenario: “Overwhelms” hospitals with up to 50,000 sick patients if social distancing requirements removed too soon and without widespread testing and contact tracing in place.
Under this projection, Tennessee hospitals by mid-May would still find themselves with "upwards of 5,000 [patients] if we don't get that transmission under control," cautioned Dr. John Graves, a Vanderbilt associate professor of health policy who helped lead efforts to construct the model.
While the state's hospital infrastructure would be stressed under the mid-range scenario, Graves said last week, it would not be catastrophic. What's needed, Graves said, is to get the infection rate below the 1-to-1 ratio.
Under the worst case scenario, Graves said "we project forward to where we lift social distancing prematurely without widespread testing and contact tracing in place" and find "the epidemic overwhelms hospital capacity by mid-May."
Graves made some of the information public Thursday during a presentation on Nashville Mayor John Cooper's livestreamed update on the crisis.
On Friday, Graves was joined by Dr. Melinda Buntin, a Vanderbilt health policy professor, in a video teleconference with reporters after relaying similar information to state lawmakers earlier in the day.
"Our model says the over 4,000 cases we have in the state of Tennessee right now could have been sparked by as a few as 10 patients six weeks ago," Buntin said. "So it doesn't take many of those cases out there going to Easter Sunday services and the like to spark a huge resurgence in cases across the state of Tennessee."
Lee remained noncommittal Thursday during a video conference with reporters when asked if he would extend his stay-at-home order in its current form.
Vanderbilt Health Policy COVID-19 Modeling for TennesseeView
It currently directs Tennesseans to remain mostly at home except for necessary tasks such shopping or similar activities, or for work. "Non-essential" businesses such as barbers and hair and nail salons are closed. The order also allows Tennesseans to exercise in open spaces, although the state has shut down its parks and some cities, including Chattanooga, have done likewise. Hamilton County parks have remained open.
"We just watch the data every day and we will make a decision before certainly it runs out," said Lee, a Republican. "We will let people know what that decision is. But data changes quickly, as you know."
Tennessee Health Commissioner Lisa Piercey pushed back on Vanderbilt's doomsday-like scenario.
"I just caution you to look at all the different models and use those as data points to inform you but not rely on those exclusively," Piercey told reporters while not mentioning Vanderbilt by name. "We're taking that same approach."
She also cited the University of Washington's Institute of Health Metrics and Evaluation model, which now projects a less dire scenario for Tennessee, with a peak coming April 19 and Tennessee's hospitals and most supplies well positioned to meet it.
As of Friday, the University of Washington model predicted that because of actions taken by the state and leaders of major cities, including Chattanooga Mayor Andy Berke, as well as mayors of Nashville, Memphis and Knoxville, hospitals can reasonably accommodate an expected surge.
It predicts that on that peak date of April 19, 1,239 hospital beds will be needed, and 241 of the state's 629 intensive care unit beds will be used. The UW projections show the state would be 205 ventilators short of the need to help the breathing of seriously ill patients with severely damaged lungs.
"It's our understanding that [the Vanderbilt] model that projects a big surge in June is contingent upon complete reversal of the current social distancing practices," Piercey emphasized. "I don't believe anybody expects that to happen."
She noted "it's really hard to predict what somewhere in the middle looks like as we think about, and as everyone in the nation is thinking about, how do we incrementally bring these [businesses] back on line."
During a teleconference call Friday with Tennessee reporters, Heather Boushey, an economist and president and CEO of the Washington Center for Equitable Growth, argued "that until we get this coronavirus under control, it will be very difficult to get back to an economy as usual.
"As long as people can get sick still in places of business or in their workplaces and so long as our health system is being overtaxed because there are just too many cases, we're not going to be able to get the economy functioning back the way we would like it to," Boushey said. "It simply won't be possible."
Vanderbilt's Graves said the university's new model has major distinctions from the University of Washington's model. For starters, it's based on state-specific data, whereas the Washington model primarily relies on data from Wuhan, China, where the first epidemic occurred, and also Italy and Spain, where COVID-19 also quickly reached epidemic levels, before arriving in the U.S., erupting in a major outbreak in a Washington state nursing home owned by a Cleveland, Tennessee, nursing home chain.
Noting China, Italy and Spain eventually cracked down with far more stringent actions than Tennessee has taken, Graves said the Vanderbilt model is fueled by Tennessee's experiences and actions, which he said fall short of those three countries' actions.
Graves said the model relies on the shown rate of infection where aggressive measures to contain COVID-19 haven't been implemented. Each infected person passes the virus on to five other people, who in turn do the same to others and so on down the chain.
The professor said that in order to "suppress" the pandemic that spans much of the globe, a transmission number less than 1.0 "must be sustained."
In his presentation, Graves said many models assume a one-time change in the transmission number as a result of policy and/or behavioral changes. Because Vanderbilt's model traces out the effective transmission number over time, the data evaluate the relative success of policy changes to date and predict hypothetical changes to the transmission number in the future.
Besides looking at the state as a whole, Vanderbilt's model also breaks down the state by eight regions and examines their transmission rates over time.
Graves also said that because rural areas are sparsely populated, coronavirus spreads more slowly, but it nonetheless spreads.
Tennessee's first known case was March 5 in Williamson County in what the model calls the multi-county "Highland Rim" region, which includes Metro Nashville.
Hamilton County and Chattanooga are identified as the "Southeast/Hamilton" region.
Vanderbilt's model shows that in the Southeast/Hamilton region, infected people were spreading the virus to an average of 4.5 other people apiece around that time. That continued for several days before starting to decline as people became more alarmed. Graves said the Southeast/Hamilton region transmission rate is down to about 1.5, currently.
Graves said the model "has to assume that only a fraction of people who are infected have been tested. And we've seen some delays and stalls in testing over the last month or so. So, I think, we are definitely not at the place right now where we have the widespread testing necessary to relax social distancing."
That's been a weekslong problem in Hamilton County, prompting the governor to visit the county this month to discuss the issue with local officials. He later stated publicly that the county lags Tennessee's other major population areas on testing.
In fact, in early April, the number of reported coronavirus tests conducted in Hamilton County was less than half the per capita rate for the state as a whole, according to state reports. Lee, and county officials, said at the time that testing is coming online that will allow Hamilton to catch up to other areas of the state.
Contact Andy Sher at email@example.com or 615-255-0550. Follow him on Twitter @AndySher1.