The shortage of testing in the U.S. may be contributing to the virus’s spread. Recent outbreaks have been worse here than in Europe, even though Europe’s vaccination rate is only modestly higher.

Stefanie Friedhoff, a professor at Brown University’s School of Public Health, recently returned from a visit to Germany and wrote on Twitter about the many benefits of rapid testing that she had seen. A friend’s husband has Parkinson’s disease, and the friend leaves a batch of tests in her hallway for people to take before they enter the home. The day care center where Friedhoff’s sister works has stayed open throughout the pandemic, because the staff and children take frequent tests.

“Imagine what ubiquitous cheap testing could do in the U.S.,” Friedhoff wrote. “It is incomprehensible how the U.S. has failed on testing.”…

For the most part, the F.D.A. still uses the same cumbersome process for approving Covid tests that it uses for high-tech medical devices. To survive that process, the rapid tests must demonstrate that they are nearly as sensitive as P.C.R. tests, which they are not.

But rapid tests do not need to be so sensitive to be effective, experts point out.