Tag: model

Vanderbilt University

This map shows new coronavirus cases by ZIP code reported over the last 10 days.

Vanderbilt University researchers have downgraded COVID-19 numbers across the state in a new report that shows an improving situation here but does not account for the reopening of the state’s economy.

Two weeks ago, researchers with the school said the state’s virus situation remained “fragile and uncertain.” That report looked ahead at when (or if) the state would need to, once again, close its economy if spikes in the virus returned and hospitals got swamped.

The new report does not contain the words fragile or uncertain. Instead, it shows just how much the data and its model have changed since the first report in early April.

For one, the April report predicted the transmission rate (the number of people infected by one person) would reduce to 1.0 by mid-May. That number was reached — statewide, anyway — by mid-April. Current transmission rates in Memphis and Nashville hover around 1.0, according to the paper. All of this changed their predictions altogether.

Vanderbilt University

“This effectively reduced the growth of COVID-19, as it meant that cases (and hospitalizations) were no longer growing exponentially,” reads the report (see below for the full report).

This pushed the predicted number of people in the hospital at one time down to around 300. As of May 11, 275 people were hospitalized with COVID-19 across the state, “not to a point of stressing hospital capacity.” Also, earlier models predicted average hospital stays of 14 days. New data shows average stays here are closer to seven days.

Vanderbilt University

While the state has seen spikes in new cases, no similar spike has been seen in hospitalizations, according to the paper. The researchers said extensive testing in Tennessee is likely the reason the two numbers aren’t more closely linked. That testing has brought new questions.

“The recent changes in testing capacity in Tennessee makes modeling COVID-19 trends difficult because the rise in the number of cases could either reflect improved detection of existing infections as testing capacity increases, evidence of an increase in transmission, or both,” reads the paper. “Teasing apart these factors has been an important focus of our work over the last few weeks.”

Vanderbilt University

However, the new figures should only be used as a baseline, said the researchers. The virus takes 14 days to incubate, and cases reported this week were likely transmitted two weeks ago, before stores, restaurants, and more were allowed to open.

“Because of this time lag, we believe it is too early to assess the impact of businesses reopening across the state or of more Tennesseans resuming activities outside their homes,” reads the report.

[pdf-1]

Facebook/Mid-South Food Bank

Volunteers load food into a car at a mobile food pantry

Tennessee’s virus transmission rate stayed the same from last week, according to Vanderbilt University researchers, and new data show what could happen when the state’s economy re-opens.

State and local officials have relied upon the Vanderbilt model in making decisions about how and when to allow citizens to return to work and some businesses. Last week, the model showed that Tennesseans had flattened the curve of the virus by staying home but said the situation here remained “fragile and uncertain.”

In a new policy briefing published Friday, researchers said Tennessee’s transmission rate remained at around 1.0. The number quantifies the average number of additional people infected by one infected person. If the number is above one, the virus is growing. A rate below one has to be sustained to suppress the virus.

“Today, Tennessee’s transmission number remains around 1.0 in both metro and non-metro areas,” reads the paper. “This indicates that social distancing has reduced transmission of the virus by limiting the number of contacts among Tennesseans.”

Governor Bill Lee plans to allow 89 Tennessee counties to re-open next week with restrictions. Six counties, including Shelby County, will remain under strict stay-at-home orders. 

Governor Bill Lee

The new Vanderbilt paper looks around the corner to what could happen next.

“This week we focus on the question of how to maximize the amount of time the Tennessee economy is ’open’ in 2020,” reads the paper. “Another way to state that same goal is that we want to minimize the amount of time spent under restrictive social distancing protocols.

“Achieving these goals means avoiding a possible second round of business restrictions triggered by escalating hospitalizations that threaten to overburden the health care system.”
[pullquote-1] The Vanderbilt model looks at what could happen if the economy is re-opened at different transmission rates. (See chart below.) If orders are lifted and virus rates spike again, it could trigger a “circuit breaker.” Stay-at-home orders could return to save hospitals and health care systems from becoming overwhelmed.

If the transmission rate continues to slow, for example, the economy could remain open indefinitely. If the state opens on May 1 and virus rates spike above 1.5, the new model says the economy would need to close again in 46 days.

All of the models boil down to this:

“The chart shows that the longer social distancing is continued, and the more transmission of the virus is reduced, the longer the economy could stay open before overburdening the state’s hospitals and risking the health of all Tennesseans who might need care, not just those suffering from COVID-19,” reads the paper.

It’s unknown if the current virus transmission rate will change after the governor’s Safer At Home order is lifted. But the Vanderbilt researchers said ”we do know that the number of social contacts among Tennesseans will increase — even if certain aspects of physical distancing at businesses, mask-wearing and hygiene practices continue.”

“Finally, we continue to stress the success of Tennesseans in reducing the transmission of COVID-19 to its current level, though we also underscore how fragile this success can be and how a transmission number below 1.0 must be sustained for the epidemic to diminish,” reads the paper. “Strong public health measures, including widespread testing and contact tracing, are essential to maintaining this trajectory as we ease social distancing practices.”

Read the new paper here:
[pdf-1]