Epidemiological models, including the ones used to create the White House estimate, rely on a certain number of assumptions and data points to reach their projections.
A grim government projection that the coronavirus could kill 100,000 to 240,000 Americans in the next couple of months may not match up with reality. The actual number of deaths could be much higher or lower depending on how aggressively states and individuals practice true isolation, experts say.
Epidemiological models, including the ones used to create the White House estimate, rely on a certain number of assumptions and data points to reach their projections. In this case, those include how many cases there are nationwide, what states are doing to limit the spread of the virus and the observed death rates.
But some of those assumptions may not reflect what is really happening, experts say.
Not all states have put strict stay-at-home orders in place. Many people might ignore the orders or fail to follow them carefully. A shortage of tests may mean the model is underestimating how bad the situation is.
The model released Tuesday by the White House could also shift for the better if social distancing proves more effective than expected.
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Although testing in the U.S. has ramped up considerably after delays and missteps, the availability of tests — and the unevenness in how they are rolled out in some states — could be masking the true number of people who have been infected nationwide and could thus affect statistical models of the virus’ impact.
“If you ask me where there are flaws in all these models, it’s from the testing,” said Dr. Kavita Patel, an internal medicine physician who was director of policy for the Office of Intergovernmental Affairs and Public Engagement in the administration of President Barack Obama. “We still, to this day, do not have an accurate estimate of the true number of cases.”
For example, in New York, the hardest-hit state, testing was limited to patients who required hospitalization — meaning mild coronavirus cases most likely were falling through the cracks in the state’s official reporting.
“We have a limited supply of tests, so we have a rationing function where the people tested today could not have gotten tested like this two weeks ago,” Patel said.
Without a known baseline, statistical models could be underestimating the true scope and severity of the health crisis.
In addition, other unknowns are associated with the White House’s forecast, because estimates of the potential death toll could shift significantly based on how well social distancing is practised in all states.
In a briefing Tuesday, Dr. Deborah Birx, the administration’s coronavirus response coordinator, and Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, outlined data on how the coronavirus could spread in the U.S. The trajectory of the statistical models influenced President Donald Trump’s decision to extend nationwide social distancing guidelines until April 30.
“There’s no magic bullet,” Birx said. “There’s no magic vaccine or therapy. It’s just behaviours — each of our behaviours translating into something that changes the course of this viral pandemic over the next 30 days.” But keeping the nation’s death toll as low as possible will require strict adherence to social distancing measures in all communities across the country, Patel said.
Although most states have enacted some form of the stay-at-home order, there were still five states — Arkansas, Iowa, Nebraska, North Dakota and South Dakota — with no such measures in place as of Wednesday afternoon. Eight states, including Texas, Pennsylvania and South Carolina, have issued partial stay-at-home orders, and some state leaders have been criticized for not having taken decisive action sooner.
In Florida, for example, Gov. Ron DeSantis has come under fire for his administration’s slow response. DeSantis announced an executive order Wednesday to limit nonessential movement after weeks of resistance, but the directive excluded religious services as an essential activity, contrary to guidelines that advocate against large gatherings.
“Even if the entire country adopted stay-at-home orders today, you’re trying to catch up from infections that were probably transmitted 10 to 14 days ago,” Patel said. “We’re constantly playing catch-up.”
But even in regions under statewide lockdowns, the effectiveness of the extreme measures depends on everyone’s doing their part, Patel said.
“There’s an unevenness to how these orders are being enforced,” she said. “It really comes down to how serious people are taking this.”
All the leading statistical models show that social distancing does slow the rates of infection. One of the most well-regarded forecasts — and one of several that the White House is using to shape its official guidance — was developed by researchers led by Christopher Murray at the University of Washington’s Institute for Health Metrics and Evaluation. They predict that if social distancing is maintained until at least the end of May, the end of the first wave of the epidemic could come by early June.
Murray’s projection, which estimates that there could be more than 93,700 coronavirus deaths in the U.S., also assumes widespread adoption of social distancing — and widespread adherence.
“In locations without social distancing measures currently in place, we have assumed they will be in place within seven days of the last model update. If not, the number of deaths and burden on their hospital systems will likely be higher than the model predicts,” officials at the institute wrote in an explanation of their methods. “We also assume that implementation and adherence to these measures is complete.”
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But epidemiological models are never static, and as updated data are fed into them, their projections can — and often do — change.
Aggressive social distancing throughout the country, for instance, could lower the estimated death toll.
“None of this is fait accompli,” said Dr. Peter Jay Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston and co-director of the Texas Children’s Hospital Center for Vaccine Development. “It’s the wrong message to send that 200,000 people are going to die — that’s a possibility, but it’s not like we’re passive players here. There’s a lot we can do as a nation.”