When six counties in the San Francisco Bay area went under a mandatory stay-at-home order on March 16, it seemed like an exceptional development in the effort to slow the spread of the coronavirus that arrived in the United States in January. At that point, there were fewer than 5,000 confirmed cases nationally, about 400 of which were in California.

Since then, of course, such orders have become commonplace. As of March 27, less than two weeks after the Bay Area’s order, more than half the country’s population was under a stay-at-home order at the statewide level. By the end of this weekend, nearly 9 in 10 Americans will be. Include localized orders, as in multiple places in Missouri, and the number tops 90 percent.

The goal of these orders is to limit the extent to which people interact with one another and, hopefully, to therefore limit the spread of the coronavirus that has now infected more than 200,000 Americans. Just because an order is in place, though, does not mean it came early enough to have the desired effect.

Our current understanding of the virus is that it manifests within two weeks of infection. The idea of isolation efforts is to keep people separated for at least that long to contain and identify where it has spread. Within two weeks of a stay-at-home order, then, assuming that it is adhered to rigidly and that testing is robust, one would expect to see a slowdown in the number of confirmed coronavirus infections.

Both of those assumptions, though, are shaky in practice. The number of tests being conducted each day in the United States has stalled at about 100,000, limiting the ability to conduct robust testing. The orders themselves have been enforced unevenly.

Consider the state of New York. It has had a statewide order in place since March 22, but the number of confirmed cases has continued to rise. By now, there are more than 400 confirmed cases for every 100,000 people in the state — the highest ratio in the country and unquestionably an undercount of the actual total.

There have been a number of states with stay-at-home orders in place where the number of cases has grown relatively slowly. California is the poster child of a successful effort to slow the spread of the virus. When it implemented its statewide order only a few days after the Bay Area was locked down, there were about three infections for every 100,000 people in the state. Since then, the number has increased, but only to about 24 infections per 100,000 people.

Illinois has not done quite as well, climbing from six infections per 100,000 residents to 55, but the state has still seen a relatively slow increase in new cases.

A number of other states with statewide stay-at-home orders have seen much faster growth. You will notice we removed New York from these graphs because its growth has been so rapid. New Jersey is on a similar trajectory; it has already grown past the upper bound of the graph. Other large states like Massachusetts and Michigan are also seeing infection rates continue to climb quickly.

Washington, the site of the first reported case in the country, is something of an anomaly. It was relatively late to issuing a statewide stay-at-home order, but other localized efforts had been successful at limiting the number of new infections.

More worrisome are states and regions which only recently enacted stay-at-home orders. Many already have much higher rates of infection relative to population, like Florida’s 32 cases per 100,000 residents. Most worrisome is Washington, D.C., where the stay-at-home order went into effect as the number of confirmed cases was at 83 per 100,000 residents — higher than the 81 per 100,000 when New York’s order went into place.

Stay-at-home orders are only one component of the effort to slow the spread of the virus, and the effectiveness of the orders depends on how they are implemented and their scale. (In Florida, Gov. Ron DeSantis (R) has mandated that the statewide order take precedence over local orders, meaning local areas cannot have stricter policies than the state itself.) Other factors, like population density, also play an important role. The states which have not yet implemented stay-at-home orders are mostly heavily rural.

The extent to which these policies worked will be measured by a very grim metric: the number of people whose deaths are related to the virus or as a result of hospital capacity being overwhelmed by patients infected with the virus. We should all hope states will rapidly shift toward the path California is on. One might fear instead that states will look more like New York.