Despite tens of millions of Americans hunkering down in their homes because of the coronavirus pandemic, the CNN debate on Sunday between Joe Biden and Senator Bernie Sanders attracted a smaller live audience than the last two Democratic matchups.

About 10.8 million people watched the candidates spar inside a closed Washington television studio, an unusual format without any in-person spectators that was widely praised for its substance and solemnity. It was the highest-rated television program of the night, just slightly ahead of “60 Minutes” on CBS.

But viewership fell short of the huge audience that tuned in for the last two Democratic debates in Nevada (19.7 million) and South Carolina (15.3 million), according to Nielsen. The NBC News debate in Las Vegas on Feb. 19, featuring Michael R. Bloomberg’s debut as a candidate, set a record for Democratic primary debates, and outscored the Grammy Awards and the Golden Globes.

The ongoing public health crisis over the coronavirus has seemingly outstripped even the presidential race in terms of Americans’ current-events interests. The Democratic field has also narrowed since the debate in South Carolina three weeks ago, with Mr. Biden establishing a consistent lead ahead of Mr. Sanders in polls.