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As a whole, the United States is experiencing its most sustained and significant decline in confirmed COVID-19 infections since the virus first reached the country last year, but the situation does vary by region. On Tuesday, the question of why cases in New York City, the original U.S. epicenter, don't seem to be declining as quickly as the rest of the country.

On Monday, for instance, New York's 14-day decline in cases was just 1 percent. Compared to the 40 percent national decline over that same period, that's pretty slow. Nobody has pinpointed a singular explanation (and there likely isn't one), but there are some simple, plausible theories you've probably heard before over the last 11 months.

The most obvious one would be testing. The city government has reportedly hinted that it considers its testing program more robust than elsewhere, so it's still picking up more mild or asymptomatic cases of the virus, generally speaking, and a big drop in hospitalizations does seem to back up that notion. Meanwhile, FiveThirtyEight's Nate Silver theorized the disparity grew even more pronounced in recent weeks because bad weather limited the number of people who could access testing in many places.

New York City Mayor Bill de Blasio addressed the question himself Tuesday, arguing that his city also was starting from a high peak. Tim O'Donnell