For days after the terrorist attacks of Sept. 11, 2001, the leading broadcast television networks dropped their prime-time sitcoms and dramatic programs and went wall-to-wall with news coverage. The round-the-clock newscasts didn’t stop for more than 90 hours, making it the longest uninterrupted news event in television history.

But with another, perhaps even more dire, national emergency afoot in 2020, the picture is very different.

As the shadow of the coronavirus has spread across the country, the networks have stuck with their regularly scheduled programs. Even a pandemic that has sickened tens of thousands and thrown millions out of work hasn’t dislodged regular airings of such programs as “NCIS,” “The Voice” and “This Is Us.”

The networks — ABC, CBS, NBC and PBS and Spanish-language broadcasters Telemundo and Univision — say they have no plans for major alterations to their schedules, although each has aired special editions of existing news programs. The most aggressive so far has been Univision, which now offers nine hours of news each day, triple the amount from before the crisis took hold.

The networks’ decision not to tamper with their prime-time schedules has kept their most lucrative programming in place. The pandemic hit at an inconvenient time — just as network television entered the final weeks of the season that ends in May, when the most climactic episodes of original shows are scheduled to air. Switching to an all-news format now would jeopardize the revenue stream generated by programs such as “Survivor” or “Grey’s Anatomy.”

At the same time, the networks’ news divisions would face logistical and financial challenges if they wanted to expand coverage. Network news staffs have been gradually pared since 2001, to the point they can’t easily muster the manpower for round-the-clock news broadcasts (though NBC and CBS could draw upon their robust cable news and digital-streaming operations, respectively). What’s more, “social distancing” mandates have complicated TV coverage of the story.

“The technical demands have never been more severe or widespread,” said Ted Koppel, the legendary TV news anchor. “It’s difficult enough for the somewhat denuded network news organizations to put on the current menu of programs. Much more would likely collapse the system.”

Granted, the virus is a qualitatively different kind of news event than 9/11 was — the former playing out as a slow-building calamity as opposed to the sudden, shocking violence of the terrorist attacks. That dynamic lends itself to the argument that coronavirus coverage is more of a marathon than the sprint of 9/11.

On the other hand, the virus is arguably the more far-reaching story, directly affecting the health, education and livelihood of virtually everyone in the nation.

And so far, public interest in news about the coronavirus has been strong. With millions of people stuck at home, ratings and readership have increased for almost every kind of news provider. The demand has helped one news broadcast, ABC News’s “World News Tonight,” achieve a rare, and perhaps unprecedented, feat: It has been the most-watched program on TV for three consecutive weeks. Five of “WNT’s” nightly broadcasts were among the six highest-rated programs on broadcast or cable last week, according to Nielsen Media Research.

Some network sources suggest the need for more news is debatable, given the development of the Internet and the broad distribution of cable news in the past 20 years.

“News coverage has completely changed since 9/11,” said Luis Fernandez, president of Telemundo Network News. Now, people who want up-to-the minute updates can get them online. “That’s the biggest difference,” he said.

But Koppel — whose signature ABC News program, “Nightline,” was born amid the Iran hostage crisis 40 years ago this week — points out that the poor and elderly are the most threatened by the virus. Yet they are also the least likely to have Internet connections and cable subscriptions, he noted, and “precisely the people most likely to remain dependent on the broadcast networks for their news.”

Representatives of ABC, NBC, CBS and PBS declined to comment on the record.

Network decision-makers are also reluctant to add more news programming for fear of preempting local newscasts and alienating the owners of their station affiliates, said a network news manager, who asked not to be named because she wasn’t authorized to speak publicly.

Former “Nightline” executive producer Tom Bettag said the “explosion” of ratings for the evening news programs clearly demonstrates that people are looking for “well-reported, well-edited summaries of what you really need to know.”

Still, said Bettag, now a journalism professor at the University of Maryland, “22 minutes is too short” to adequately cover a story as important and sweeping as the virus pandemic.

“Every correspondent will tell you he or she begged for a little more time to give room for nuance and especially for fact checking,” he said. “These are complicated issues. When the anchors turn to their medical experts now, it’s is usually for one question, maybe two. It would take a war with the [station] affiliates to get them to give up local news time, but those broadcasts should go to an hour. This is a national emergency perhaps greater than 9/11.”

Still, Bettag doesn’t think a lot more news programming is necessary.

“There is such a thing as coronavirus fatigue,” he said. “I’m pretty sure people, shut in as they are, need good distractions. . . . All coronavirus, all the time? Spare me.”