He did, however, go to the window and wave silently to a mere several hundred people in the huge square, which often draws tens of thousands. Most kept a safe distance from each other as they watched the pope deliver the address on four mega-screens.
"It's a bit strange this Angelus prayer today with the pope caged in the library, but I see you and I am close to you," he said.
It was the first time that Francis had skipped giving the blessing and reading an address from the window since his election in 2013, apart from times he was traveling outside Rome.
Francis appeared to have recovered from a cold that forced him to skip a Lenten retreat with senior Vatican officials near Rome last week.
"I am close in prayer to people who are suffering because of the current coronavirus epidemic as well as to all those who are taking care of them," he said, speaking while standing in the frescoed room which is used mostly for private audiences.
He encouraged the faithful "to live this difficult moment with the strength of faith, the certainty of hope and the fervor of charity." The window was then opened, and he waved briefly and silently.
Some pilgrims had come a long way hoping to get the blessing directly.