In repeat remarks, Gov. Andrew Cuomo has been strident: The peak of the coronavirus outbreak in New York State will hit “about 45 days” from now, he said.
But epidemiologists who study the spread of infectious disease are a little more circumspect. There is simply too much uncertainty around coronavirus and Covid-19, the disease it causes, to accurately predict a peak caseload date, they said.
To further complicate matters, the State Department of Health declined to specify where the governor’s estimates came from, instead attributing them to “health experts (and) epidemiologists.”
That may contribute to further public confusion at a time when many already feel overwhelmed.
“I think the governor and New York State are taking the right actions in asking people to do their part and in protecting the most vulnerable in the state,” said Dr. Shweta Bansal, a mathematical biologist at Georgetown University who models the spread of infectious diseases. “However, I can't say we know enough right now to make any predictions on when this will end.”
Cuomo first referenced the “45 day” peak at a March 17 news conference. Later that afternoon, he repeated the figure during a taping of the New York Times’ podcast "The Daily," which aired a day later.
“If you look at the speed, the increase in the rate, the spike in the increase of the number of cases – we're looking at a possibility of an apex being about 45 days away,” he said.
“That’s one projection, 45 days,” he later added.
On Saturday, Cuomo gave a less specific timeframe, warning that the crisis surrounding coronavirus could last "months." "I don’t believe it’s going to be a matter of weeks," he told reporters. "It's going to be a matter of months."
But it’s unclear who produced the 45-day peak projection and what variables they did or did not account for. That’s significant, said two epidemiologists, because disease models produce different peaks depending on their underlying data and assumptions.
In response to questions from The Buffalo News, a public information officer for the state Department of Health said only that “two groups” had conducted Covid-19 modeling for the state and that both calculated “similar answers” as to when the peak would hit.
In remarks Wednesday, Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, cautioned against forecasting a date for peak caseloads, though he called New York’s project “possible” and “not unreasonable.” (The U.S. Centers for Disease Control and Prevention did not respond to inquiries about the projection.)
“Things are changing all the time, and multiple groups have predicted (different peak dates) in different settings,” said Dr. Derek Cummings, an infectious disease epidemiologist and professor of biology at the University of Florida. There are “multiple sources of uncertainty,” he added, in all of the models.
Those uncertainties include basic characteristics of the emerging disease, such as the role that young and asymptomatic people play in its transmission, Bansal said. Widespread problems with testing, both in New York State and across the country, also mean scientists have little concrete notion how many people are already infected or at what rate the virus has spread.
And because there is an inherent delay between when people become infected and when a test confirms that diagnosis, estimates on both caseload numbers and the rate of transmission are outdated the moment public health officials report them.
“You’re always looking at what the outbreak was,” Cummings said.
On top of that, scientists don’t yet understand how warmer temperatures will influence the spread of the disease, Cummings added, nor to what extent interventions such as social distancing or increased hand-washing will slow transmission. Aggressive mitigation measures, such as the ones rolled out in New York this week, are designed to "flatten the curve," or push the peak caseload later.
One recent and widely cited analysis, produced by Imperial College London, predicted that different mitigation measures could delay the peak by as many as three weeks in the United Kingdom. Meanwhile, the United States will hit its peak caseload in June at the earliest – more than 70 days from now – the paper predicted.
“However, there are very large uncertainties around the transmission of this virus, the likely effectiveness of different policies and the extent to which the population spontaneously adopts risk reducing behaviors,” its authors wrote. New York's Department of Health did not answer questions about the level of mitigation assumed in the models Gov. Cuomo has recently referenced.
Absent those sorts of details, scientists say, New Yorkers probably shouldn’t count the days until May 1. But they should, argued Bansal, interpret Cuomo’s remarks as a “call to action.”
“The outcome of this outbreak ... very much depends on our ability to respond,” she said. “The faster we take action to social distance and limit transmission as individuals, the more the outbreak's consequences can be diminished.”