The response to the novel coronavirus (COVID-19) in the United States has changed dramatically over the last week, with President Trump declaring a national emergency and multiple states and cities essentially going into lockdown. One thing that hasn’t changed: the U.S. is still short on coronavirus tests. While the administration says supply has increased, many sick Americans are still having trouble finding a way to know if they have coronavirus.

There were clear benefits to robust testing early in the spread of the virus. But now that we’ve missed that window, it might seem like testing is less of a priority, at least in areas where the virus is already widespread. After all, if we’re all behaving as though everyone around us already has COVID-19, as New York City officials reportedly told U.N. delegations they should, why do we need to know who actually does?

But there’s still much that can be learned — and lives that could be saved — by increasing testing across the country immediately. And in fact, the social distancing measures being taken right now are as much to make up for not testing sooner as they are to slow the virus’ spread. Here are four ways that widespread testing is still a critical step in our coronavirus defense:

1. Testing helps allocate resources

“This is basic disease surveillance,” said Gregg Gonsalves, a microbial disease epidemiologist at Yale University. “We can’t begin to control this epidemic unless we know where this is and how many cases we’ve got.”

Gonsalves said testing tells officials where to allocate resources. We do not have an unlimited supply of things like ventilators, which can be used to help treat severe cases of the infection. If we know which areas will be hardest hit now and in the weeks to come, we can allocate federal funds and supplies to those areas so they’ll be able to administer better care, Gonsalves said.

And while it may seem obvious that a densely populated area like New York City is likely to have a higher infection rate than a county in rural Montana, Gonsalves said population is not a good enough predictor of where the disease will strike hardest or first.

“It could be New York. It could be L.A. It could be Chicago. It could be St. Louis,” Gonsalves said. “Population isn’t a great way to predict who will have the greatest number of cases per capita.”

2. It saves time and equipment in hospitals

Along with allowing us to better allocate resources, knowing who is or is not infected with the virus will allow hospitals to use the equipment and supplies they already have more efficiently, according to Dr. W. Graham Carlos, chief of internal medicine at Eskenazi Health in Indianapolis.

“When somebody comes into the hospital who does not have a known positive diagnosis, we have to rule it out,” Carlos said.

While waiting for test results, patients have to be treated as if they are infectious, Carlos said, meaning health care workers have to use personal protective equipment like gowns, gloves and face masks whenever dealing with that patient. If a patient doesn’t have COVID-19, those supplies could have been saved for someone who does.

If widespread testing was done outside of a hospital setting — such as at drive-through test sites like in South Korea — it would save not only equipment, but valuable time for hospital workers treating critical patients, Carlos said.

“If we already know you’re positive, that saves time too,” Carlos said. “We have treatments coming online and we may be more apt to do those things if we have a diagnosis already.”

3. It makes social distancing more effective

Social distancing, a now-ubiquitous term many of us had never even heard of until just a few weeks ago, has been one of the main tools deployed to help slow the spread of COVID-19 and “flatten the curve” of its impact.

But social distancing is a voluntary practice, one that many Americans can’t, or won’t, observe right now. One way to encourage more people to stay home, or governments to start shutting things down, is telling Americans exactly how bad the outbreak is. While many places in the U.S. have started enacting measures to limit social gatherings, like closing bars, restaurants and theaters, it’s not a universal practice. Without knowing where the virus is spreading, we can’t say whether the municipalities that ought to be shutting down are doing so.

There’s also the fact that, eventually, we’re going to want to go back outside again. As the current protocols start to relax, a second wave of infections may arise, especially if we don’t have a good grasp on where and how many cases we have in the U.S., said Dr. Eli Perencevich, a professor of medicine and epidemiology at the University of Iowa.

“We can’t stay in social distancing forever,” Perencevich said. “So we need to ramp up testing quickly.”

Perencevich and Gonsalves both said the current measures are really a way for us to make up for the time lost by not having widespread testing sooner. They said that if we don’t rapidly scale up testing now, all this staying at home and canceling sports events may be for naught, because we still won’t know how bad the outbreak is and won’t be able to respond appropriately. Staying inside gives us the opportunity to get caught up on testing, an opportunity these experts don’t want to squander.

“We’ve been out of the containment phase for a month, “ Gonsalves said. “This is no longer about bending the curve in terms of number of infections. We won’t bend the curve of the number of infections. But we might bend the curve of the number of deaths.”

4. It provides helpful data going forward

While it’s hard to imagine right now, eventually we will be through the worst of this pandemic. At that point, our attention will start to turn from emergency measures to long-term responses, like what treatments or vaccines might help protect us from COVID-19 outbreaks in the future, and how we can avoid similar pandemics.

To make any of those predictions, we need data — and the most basic information we’ll need is knowing how many people were infected and where.

“When we look at this retrospectively, knowing that is going to be important,” said Tara Smith, an epidemiologist at Kent State University. “The data we need to look at the genomics of the virus, who transmitted to whom, who sparked clusters in new areas, we get all of that data from testing.”

This can also help us measure how effective different measures are at combating this kind of viral outbreak, Smith said.

But in order to get a solid grasp on the spread, we need to drastically ramp up testing. Currently, just under 59,000 tests have been completed in the U.S., according to The COVID Tracking Project, a database created by Related Sciences and The Atlantic. Compare that to South Korea, where 10,000 people can be tested every single day.

While testing is scaling up, we’re still not there yet. The American Clinical Laboratory Association said in a press release last week that as more commercial labs come online, they will be able to exceed 280,000 tests per week, but won’t reach that full capacity until April 1. Quest Diagnostics, a private lab company that is currently scaling up operations, said it expects to be able to perform 10,000 tests per day by the end of the week and 20,000 tests per day by the end of the month.

Smith said that’s the scale we ought to be operating at in order to get the needed data.

“We’re bigger than South Korea. We have a higher population and we should have the technical capacity to do this,” Smith said. “But we are so behind the curve.”