The feverish race for a coronavirus vaccine got an infusion of energy Wednesday as Johnson & Johnson announced that it has begun the final stage of its clinical trials, the fourth company to do so in the United States as the country hits a grim milestone of 200,000 deaths from the pandemic.

Johnson & Johnson is a couple of months behind the leaders, but its advanced vaccine trial will be by far the largest, enrolling 60,000 participants. The company said it could know by the end of this year if its vaccine works.

And its vaccine has potentially consequential advantages over some competitors. It uses a technology that has a long safety record in vaccines for other diseases. Its vaccine could require just one shot instead of two — important considering that the entire population of the world needs vaccination. And it does not have to be kept frozen as it is delivered to hospitals and other places where it will be given to patients, simplifying the logistics of hundreds of millions of doses.