Officially, the novel coronavirus arrived in New York City on March 1 with a 39-year-old Manhattanite returning from Iran. But given that testing was not widely available before that first confirmed case was reported, it’s hard to tell exactly when the outbreak in New York began--or how far it spread before it was detected.

One possible answer comes from researchers modeling the international spread of the disease at Northeastern University. According to estimates they released Thursday, 10,700 New Yorkers had already been infected with COVID-19 by the time the city’s first case was reported. Adding the estimates from New York City with those from San Francisco, Chicago, Seattle and Boston, the researchers estimated there had been 28,000 cases of COVID-19 in major U.S. cities by March 1st--a far cry from the 23 that had been reported in the entire country at that time.

Dr. Alessandro Vespignani, who led the research team at Northeastern, said he and his team tried to warn officials in the U.S., the U.K., Italy, and Spain early on that the disease was spreading undetected but were paid little mind. “They told me, ‘OK, that’s happening on your computer, not in reality,’” he told the New York Times.

Some epidemiologists said the early, undetected spread of coronavirus modeled by the researchers at Northeastern was in line with their own analyses and sounded reasonable, while others said the figures sounded higher than they would have expected.

These figures arrive at a time when people are trying to establish new sources of information to bring the still somewhat blurry picture of the coronavirus’ spread in the U.S. into sharper focus. Just this week, new autopsy reports from California revealed that two people who died in early and mid-February, respectively, were positive for coronavirus; the first coronavirus death in the U.S. was previously placed in Washington state on February 29th. The news prompted California Governor Gavin Newsom to order medical examiners and coroners in the state to review autopsies from as far back as December.

Meanwhile, Governor Andrew Cuomo is pushing to ramp up antibody testing in New York to get a better sense of how many people have already been infected with the disease and recovered, in the hopes that he can gain enough perspective to carve a path forward.

For those who are curious, an interactive version of the Northeastern model online makes it possible to not only look at past and future projections for the spread of coronavirus in the U.S., but also to compare projected outcomes with reality.

The model’s projection for the total number of deaths from coronavirus in the U.S. so far, given all the mitigation measures that are in place to slow the spread of the disease, is actually lower than the reported number of deaths--but it’s not far off. The model projected 47,174 deaths nationwide as of April 23; the reported figure as of Thursday was more than 48,000 (without mitigation efforts, the model estimates there would have been 299,000 deaths in the U.S. by April 23rd).

By the model’s estimation, there should have been 467 new deaths in New York state on April 17th; in reality, 540 were reported.

Assuming mitigation policies remain in place, the model projects that a little under a month from now, on May 18th, the daily count of new deaths in New York will have plummeted to 94.

Of course, these projections can’t take into account all of the variables that make life messier than a model.

“There are large uncertainties around the transmission of COVID-19, the effectiveness of different policies and the extent to which the population is compliant to social distancing measures,” the Northeastern team notes in a disclaimer on its website. “The presented material is based on modeling scenario assumptions informed by current knowledge of the disease and subject to change as more data become available.”