COVID-19

It begins with a mild fever and malaise, followed by a painful cough and shortness of breath. The infection prospers in crowds, spreading to people in close reach. Containing an outbreak requires contact tracing, as well as isolation and treatment of the sick for weeks or months.

This insidious disease has touched every part of the globe. It is tuberculosis, the biggest infectious-disease killer worldwide, claiming 1.5 million lives each year.

An experimental coronavirus vaccine developed by Johnson & Johnson protected monkeys from infection in a new study. It is the second vaccine candidate to show promising results in monkeys this week.

The company recently began a clinical trial in Europe and the United States to test its vaccine in people. It is one of more than 30 human trials for coronavirus vaccines underway across the world. But until these trials are complete — which will probably take several months — the monkey data offers the best clues to whether the vaccines will work.