There is a cheap, simple way to control Covid-19. Writing in the New York Times the other day, Boston University economist Laurence Kotlikoff and Harvard epidemiologist Michael Mina say it could put America quickly back to work. But we are not using it.

Here is how it works. With paper-strip tests, Americans could test themselves every day in their own homes, at a cost of $1 to $2 per test. The government could even make the tests available for free.

Unlike lengthy swabs and finger prick tests (which cause personal discomfort), paper strip testing involves no more than spitting into a tube or the use of a short nasal swab—with results in a few minutes.

By contrast, the standard PCR test currently being used costs from $50 to $100 and sometimes more. Results can take more than a week—and that makes them virtually useless. Also, testing tends to be a one-time, irregular event.

Widespread use of strip tests could solve our lockdown problem in the following way:

• Employers could require their workers to take time-dated photos of their negative test results before coming to work.
• Restaurants and bars could limit their customers to those who have a negative-test photo.
• Schools and colleges could admit students and airlines could accept passengers based on that day’s negative-test photo.
• Sports arenas, concert halls and movie theaters could do the same.

So, what’s the holdup?