When New York City’s Covid-19 epidemic peaked in late March and early April, the city was reporting more than 5,000 new confirmed cases a day, and more than 60% of tests for the disease were coming back positive. In Arizona, which has a similar if somewhat smaller population (7.3 million versus 8.3 million), new cases are currently averaging about 3,000 a day and about 20% of tests are positive. Things may keep getting worse in Arizona, and its Covid outbreak may eventually surpass New York City’s. But it’s a long, long way from getting there, and I’m guessing that it won’t. That isn’t to say that things are looking good in the Grand Canyon State, or in Texas, Florida, Southern California or any of the other places now experiencing big growth in coronavirus cases. But the specific conditions that enabled the awful explosion of the disease in New York City are not being replicated. The most important of those conditions was a near-total lack of awareness and understanding of what was going on until it was way too late. By the beginning of March, when New York’s first Covid-19 cases were confirmed, more than 10,000 people in the city may have already been infected, according to a modeling exercise conducted in April. With a reproduction number (the number of people each person can be expected to infect) that has since been estimated at above six in late February and early March, that total subsequently exploded. A new study of blood samples taken from non-coronavirus patients at Mount Sinai Health System hospitals in the city indicates that as many as 800,000 New Yorkers may have been infected by the week of March 16, when the city closed schools and many began working from home (the state’s stay-at-home order went into effect March 22). The second half of March was also when testing for the disease began to get off the ground in a big way, but by that point demand was so overwhelming that only those with severe cases or underlying conditions could get tested, hence the sky-high positivity rates. By mid-April, according to an antibody survey conducted by the state at the end of the month, 1 about 1.7 million New Yorkers (20% of the city’s population) had contracted the disease, or 12 times the number of confirmed cases up to that point. In Arizona, more than 15,000 people are now being tested daily — a level that New York City didn’t reach until May. The percent testing positive has risen from 9% to 20% over the past month, a sign that the testing isn’t adequate to keep up with the spread of the disease. But Covid-19 is not raging out of control as it was in New York in March, at least not yet. Data scientist Youyang Gu, creator of one of the better coronavirus forecasting models out there, estimates that 330,028 Arizonans had contracted the disease as of July 1, about four times the confirmed-case number. Although the Trump administration’s repeated claims that the recent upturn in confirmed cases is due entirely to increased testing are wrong, the big increase in testing does imply that this upturn probably isn’t as big as that of March and April. The thinking is that higher positive test rates equate to more missed cases, although the true relationship is unlikely to be exactly as shown here. On a national level, my formula delivers plausible-ish results, showing 29.6 million Americans, or 9% of the population, infected so far, a little less than twice Gu’s estimate, which is based on deaths from the disease, and a ratio of estimated cases to confirmed ones of 11.5, not far from the 10 times higher recently suggested by Centers for Disease Control and Prevention Director Robert Redfield. Apply it to New York City’s testing data, though, and you get a total of 10.3 million infections, which seems a bit high for a city of 8.3 million inhabitants. In any case, the basic message that Covid-19 cases were much more severely undercounted in March and April than they are now is almost certainly correct. The Sun Belt outbreaks are thus of a lesser speed and scale — so far, at least — than those that hit New York and a few other metropolitan areas in spring. What comes next is, of course, the big question. I’m no epidemiologist, and even epidemiologists have struggled mightily to predict the effect that differing degrees of social distancing, testing, contact tracing, quarantining and other public health measures have on the spread of Covid-19. In a totally naive population, with no access to testing and no habit of wearing face masks, it can spread shockingly fast. If everybody stays home, it hardly spreads at all. In between are countless potential combinations of public policy and individual behavioral changes with impacts that are extremely hard to model. It does seem safe to assume that we won’t see the sharp drop-offs in new infections that have occurred in New York and other early Covid-19 hotspots since April. The draconian measures that enabled them aren’t going to be repeated, and the new outbreaks are both too big to be controlled just with contact tracing and quarantining and too small to have rendered a significant share of the population at least temporarily immune to the disease. Still, I’m willing to bet that the Sun Belt outbreaks won’t keep spiraling out of control either. Recent reproduction numbers in these states have been estimated in the 1.2 to 1.4 range, not the 6-plus that may have prevailed in New York early on. States and cities are cracking down on some of the likeliest channels of disease spread, such as bars. Republican opposition to mask-wearing is fading, at least among elected officials and Sean Hannity. Perhaps most important, once people actually know others who have become ill with the disease they tend to take it a lot more seriously and adjust their behavior accordingly. In Harris County, Texas (home of Houston), one of the first places to raise alarms in this wave of infections, new cases appear to be on the decline. If the same happens in other hot spots in Texas, Arizona, California, Florida and elsewhere in coming weeks that will be welcome news, but it won’t be much of a victory. Hospital intensive-care units will probably still hit capacity. Tens of thousands of Americans will die unnecessarily. New York City’s Covid explosion in February and March was the product of a spectacular failure of imagination and governance in the wake of similar disasters in Wuhan, China, and Northern Italy. Today’s Sun Belt outbreaks are the products of failures less spectacular but in some ways more maddening, given the great advances since early March in testing capacity and knowledge about how the disease spreads. The choice now isn’t between opening the economy and letting Covid-19 rage. It’s between implementing a few targeted policies (indoor mask-wearing; restrictions on bars and other indoor settings most conducive to transmission; investments in contact tracing and other public-health efforts) that could probably bring the disease under control, and just letting it continue to spread like this — dragging down the economy the entire way — until we have vaccines and better treatments. Bloomberg