A push to greatly expand contact tracing

No matter how well we all practice social distancing, Covid-19 is unlikely to completely disappear. So to safely return to something like normalcy, society needs to be able to spot and swiftly contain new cases that pop up.

Rapid, widespread testing, once it becomes available, is the key to the spotting part. But since people can spread the virus before they know they have it, effective containment depends both on isolating those who test positive and on checking everyone they’ve come in contact with recently.

That’s why public health officials say robust contact tracing is a must for reopening the economy, which President Trump hopes will start happening by May 1. But it will be a huge, expensive job.

Mr. Trump is expected to announce as soon as Thursday evening that the Centers for Disease Control and Prevention will hire hundreds of workers to perform contact tracing, and that the federal government will help states pay for their own expanded efforts.