We're fighting the greatest public health crisis in a century, and we barely understand our enemy, Axios' Felix Salmon writes.

• We cannot afford to stay in lockdown until a cure or vaccine arrives — but anybody trying to reopen our cities needs information that is frustratingly difficult to find.

The big picture: The single biggest obstacle to reopening the economy is a lack of visibility — we don't know the scope of the pandemic itself, or its economic fallout, or how its trajectory will change as we embark upon an ad hoc effort to reopen the economy.

We don't know how many people the coronavirus has killed, or how many people have had it.

• The official tally of over 37,000 deaths is too low, because it's based on people who died after testing positive for the coronavirus, but we don't know how low.

We don't know how many Americans have lost their jobs because of the coronavirus shutdown.

• The official tally is 22 million new applications for unemployment benefits. But millions more haven't been able to make it through the application process, or haven't tried.
• The biggest employers will be able to rehire their legions of workers, but the bigger concern is the businesses that will never be able to reopen. We don't know how many of them there will be.

We don’t know when we'll have a treatment, whether summer will tame the spread, or whether the virus could return in the fall even stronger. We don't know whether we're immune once we've had it, or for how long.

• We don't know whether tech will allow us to trace it, or whether enough Americans would sign up for that, even if it does.
• We don’t know when it’ll be safe to fly, go to a game, or pack into a school or a church. 

The bottom line: It’s shocking and a bit scary how much we do not know, despite how much we now do know.

Governors and mayors are walking a political tightrope as they decide how quickly to reopen their economies, Axios’ Alayna Treene and Stef Kight report.

The fear: Opening up too fast would only require a fresh set of lockdowns later.

• "That would be like releasing someone from prison, and then saying, 'Sorry, you need to come back to serve more time,'" Paul TenHaken, the Republican mayor of Sioux Falls, South Dakota, tells Axios.

Yes, but: Republican governors in particular will likely face considerable political pressure to open up as quickly as possible — which could put them at odds with mayors in their state.

• TenHaken issued a "Safer at Home" proclamation for his city, which has a high share of the state's rising number of COVID-19 cases. But South Dakota Gov. Kristi Noem has refused to enact a statewide order.

Between the lines: Although President Trump’s formal guidelines leave most of these decisions up to local officials, he has also tweeted criticisms of Democratic governors’ continuation of stay-at-home orders.

• Protests against the restrictions are also cropping up.

“I'm very concerned about any type of pressure — political or otherwise — to make hasty decisions based on the economy as opposed to the science,“ Tampa Mayor Jane Castor tells Axios.

• She pushed for a shelter-in-place order for her city long before Florida Gov. Ron DeSantis issued one statewide, and DeSantis has already loosened some of those restrictions in the days since the White House released its reopening plan.

Read more.

Detroit Mayor Mike Duggan announced yesterday that the city will start making diagnostic tests available to all employees of “essential” businesses, and to city employees performing essential services.

• It’s the first program of its kind, and a model for other cities to follow. And it’s a reminder that testing remains the limiting factor in every facet of our response to the coronavirus, Axios' Sam Baker writes.

You may be tired of hearing about testing. You may think it has become an almost myopic focus in a multifaceted crisis. But there is simply no way to work around it, or to put that problem to the side and focus on something else. All roads lead back to testing.

Between the lines: Detroit’s plan to test people who aren’t experiencing symptoms, even if it's just a small group, is critical.

• Many parts of the country, though, simply don’t have the capacity to test anyone who isn't feeling sick. That will never be good enough.
• Although more rapid tests are becoming available, turnaround times of up to a week increase the risk that people will spread the virus without knowing it.
• If you test someone too soon after they’ve contracted COVID-19, they won’t have enough of the virus in their system, resulting in a false negative — which means some infected workers may slip through the cracks even with widespread testing.

Our thought bubble: Every incremental step that brings more people out into the world creates some level of additional risk. We don’t have a vaccine and we can’t stay inside forever, so all we can do is try to find a level of risk that’s manageable.

• The only way to manage that risk is to stay on top of the virus’ spread, and the only way to do that is with testing. And so the limitations in testing will always, necessarily, restrict everything else we try to do.

Every treatment has some side effects — including social distancing.

Prolonged isolation, coupled with sustained job losses, could increase the risk of depression, as people are removed from the community support system that keeps them going, Sam writes.

• That could in turn increase the risk of suicide, as a recent opinion piece in JAMA Psychiatry explains.
• "A grim tradeoff is already being made between saving different lives: Saving the lives of those who are most vulnerable to COVID-19 versus saving the lives of those who are most vulnerable to suicide, substance abuse, and domestic violence," experts at Johns Hopkins write.

What to watch: Virtual check-ins are all the more important here — from simply keeping in touch with friends and family, to online support groups, to telehealth visits with mental health professionals.

None of this means social distancing was a bad idea, or that it needs to end quickly — it's definitely less deadly than the coronavirus. But even the most necessary interventions still need some careful management.

The National Suicide Prevention Lifeline (1-800-273-8255) provides 24/7, free and confidential support for anyone in distress, in addition to prevention and crisis resources. Also available for online chat.

Lab scientist Alicia Bui tests the blood of patients who have recovered from the coronavirus, looking for antibodies that prove exposure and may confer immunity to the virus.

• These serology tests will likely be an important part of getting high-risk employees, especially health care workers, safely back to work.

Axios' Rashaan Ayesh is answering readers' questions about the coronavirus. Drop us a line at [email protected].

Q: What are the best practices for reusing face masks?

• The FDA recommends using cloth masks, not N95s, and the CDC advises laundering them in a washing machine with detergent.
• The University of Utah says cloth masks should be washed in 160°F water with soap or detergent, and recommends soaking them for five minutes in a bleach solution.

Q: What is the best way to keep up with appointments like physical therapy?

• The American Physical Therapy Association recommends rescheduling non-urgent in-person care. Some specialists are using telehealth and videoconferencing to work with patients.

Q: Can I offer or accept home-cooked foods or share books?

• Consult the CDC's social distancing guidelines in deciding how best to be a good neighbor.
• Apps like NextDoor form digital groups that can connect you with neighbors.

Q: How long should I self-isolate after testing positive?

• As always, ask your doctor. The CDC says people who've tested positive need to isolate at home for at least seven days after symptoms first appeared, wait at least 72 hours after fever is gone, and hold off until respiratory symptoms have improved.

Q: Can I microwave or freeze my food to kill the virus on the packages?

• The FDA says there's no evidence of food packaging or food being associated with coronavirus transmission. There also isn't "direct data for a temperature-based cutoff for inactivation" for the virus, per the CDC.

Many renowned educational and cultural institutions are meeting Americans where they are — at home — with a slew of new intellectual pursuits even in a time of lockdowns and social distancing.

What's happening: Whether you're looking for an intensive 40-hour course or a short video on art history for your lunch break, you may have more options than ever before, Axios' Naomi Shavin writes.

Some highlights:

• Ivy League schools are offering a combined 450 free online courses, and many other universities around the world are also putting popular courses online for free. Some 1.5 million people have already registered for Yale's famous happiness course.
• New York's Museum of Modern Art is offering free classes that include "What is contemporary art?" and "Fashion as design."
• The Barnes in Philadelphia borrowed a page from restaurants' playbook to launch "Barnes Takeout," a series of short online lectures that focus on a single work of art.
• From symphony halls to Broadway theaters, performance venues are streaming past performances and informational talks.

If the life of the mind gets to be too much, high-end gyms and exercise programs have made headlines for offering free online videos, too.

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