Why do the COVID-19 models keep changing?

From the time the first case of COVID-19 appeared in the United States, estimates for the final number of infections and related deaths have fluctuated greatly.

In late February, President Donald Trump was assuring the country that the disease would all but disappear. By mid-March, though, the growing pandemic was overwhelming the nation’s hospitals.

The health experts charged with crafting the US’s coronavirus response have warned Americans that any modeled estimates will necessarily be flawed. Virus models rely on a host of variables and can only be so accurate, especially if social distancing measures are not followed.

With the estimates having changed dramatically over the last two months, it is easy to think that they don’t serve a purpose. However, the models, even when they must be adjusted, help health experts and policymakers respond to the pandemic.

“Down to close to zero”

On February 26, Trump made a statement that would lead to much criticism and ridicule in the weeks afterward:

“And again, when you have 15 people, and the 15 within a couple of days is going to be down to close to zero, that’s a pretty good job we’ve done.”

This statement was made during one of the first of many public briefings on the pandemic, alongside Vice President Mike Pence and members of the Coronavirus Task Force. At the time, the US only had 15 official cases of the disease.

In the briefing, Trump touted his decision to enact a travel ban on parts of Asia as the reason there were so few cases. He said he had been “ridiculed” for his choice but that “it turned out to be a very good thing.”

However, as reported by Reuters, that travel ban likely came too late to have been effective in stopping the spread of the virus. In the weeks after the White House first learned of the epidemic, but before it enacted its ban, an average of 14,000 travelers arrived from China daily, including the individual who would turn out to have the first confirmed case of COVID-19 in the US.

On February 29, the US had its first COVID-related death. From there, the rate of spread quickly accelerated.

Possibly millions dead

In 2019, before COVID-19 had emerged onto the global stage, a scientist named Eric Toner completed a hypothetical model of coronavirus spread at John Hopkins Center for Health Security. Toner’s model predicted that up to 65 million people around the world could die. At the time his model was made public in late January 2020, less than 100 people had died of COVID-19, all in China.

In late February, prior to Trump suggesting that cases could soon drop to zero, a disease modeler for the Centers for Disease Control and Prevention (CDC) estimated that up to 214 million people in the US could be infected, with the number of deaths between 200,000 and 1.7 million. This estimate, which was presented to CDC officials, did not account for preventative social distancing measures.

By mid-March, both the state and federal governments were acting to slow the spread of the virus, which had killed 50 people in the country. Trump declared a National Emergency on March 13, two days after the World Health Organization (WHO) officially declared the virus a pandemic.

March 13 was also the day the US enacted a travel ban from mainland Europe. Days later, it was reported that New York City Mayor Bill de Blasio was considering a citywide lockdown.

On March 19, all of California was placed under a stay-at-home order. On March 20, New York Governor Andrew Cuomo issued a similar statewide order. Illinois went under lockdown on March 21.

Nonetheless, before the end of March, the US would have the most confirmed cases in the world.

100,000 to 200,000 deaths

On March 29, while speaking on CNN, Dr. Anthony Fauci, a member of the Task Force, said modeling showed 100,000 to 200,000 Americans could die of the virus. At that time, fewer than 2,200 people had died.

Fauci acknowledged that the new modeling, based on the effective implementation of social distancing measures, had dropped the original worst-case scenario estimate considerably. However, he warned that such estimates should not be taken as a guarantee, and he didn’t “want to be held to that [estimate].”

“It’s such a moving target,” Fauci said of a potential death total, “you could so easily be wrong and mislead people.”

Fauci said the models “are only as good as your assumptions.” The doctor explained that the models give a best-case scenario and a worst-case scenario and “generally, the reality is somewhere in the middle.”

From 60,000 to 74,000

Despite his caveats, Fauci still faced criticism after he lowered the estimate once again on April 9. Speaking to NBC’s Today Show, Fauci said the likely total deaths would be closer to 60,000 rather than 100,000.

Supporters of Trump claimed that Fauci had intentionally overestimated possible deaths in order to shut down the country and hurt the president politically. Popular conservative talk radio host Rush Limbaugh called Fauci a “Hillary Clinton sympathizer,” referencing Trump’s Democratic opponent in the 2016 election. The hashtag #FauciLied has spread on Twitter ever since.

However, with many states reopening or planning to do so, total US deaths passed 60,000 on April 29, greater than the total number of Americans who died in the Vietnam War. On April 27, an updated model put the number of expected deaths at just over 74,000 by early August.

In the face of this potentially substantial death count, Trump has maintained an optimistic view, stating of the virus on Wednesday, “It’s going to leave. It’s going to be gone. It’s going to be eradicated.”

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