Just as the United States seems to have emerged from the worst of a surge in coronavirus cases that ravaged the country for months and peaked after Americans crowded indoors for the winter holidays, public health officials are concerned about another potential superspreader date: Super Bowl Sunday.

January was the country’s deadliest month so far in the pandemic, accounting for 20 percent, or 95,246, of the more than 460,000 coronavirus deaths the United States has recorded in the past 12 months. That’s more people than could fit into even the largest N.F.L. stadium.

Experts worry that football fans gathering on Sunday in Tampa, Fla., for the championship game between the Kansas City Chiefs and the Tampa Bay Buccaneers, or at watch parties across the country, could set back the nascent progress of recent weeks. The daily reports of new cases and deaths remain high but have fallen somewhat. The seven-day average of new case reports in the U.S. dropped to 125,804 on Friday, the lowest level since Nov. 10. Reports of deaths, a lagging indicator because patients who die from Covid-19 generally do so weeks after being infected, averaged 2,913 a day, the lowest rate since Jan. 7.

The United States is administering 1.3 million vaccine doses a day on average, as the Biden administration pushes to speed distribution before more contagious variants that might evade vaccines can become dominant. The N.F.L. has offered President Biden all 30 of its stadiums for use as mass vaccination sites.

Officials like Dr. Anthony S. Fauci, Mr. Biden’s chief medical adviser for Covid-19, have warned Americans against gathering for Super Bowl parties with people from other households, especially in places without ideal ventilation.

“You’re really putting yourself and your family in danger,” Dr. Fauci said Friday on MSNBC.

“It’s the perfect setup to have a mini superspreader event in your house,” he added. “Don’t do that for now.”

While health experts worry about a rise in cases after the game, some said they don’t anticipate anything as deadly as the post-holiday wave that peaked in January. That is because Thanksgiving and Christmas tend to spur more domestic travel than the Super Bowl does, said Dr. Catherine Oldenburg, an infectious disease epidemiologist at the University of California, San Francisco.

Still, even parties pose a threat, said Carl Bergstrom, a professor of biology at the University of Washington.

“My sense is that it’s a really great year to watch it at home with your family, and not go to Super Bowl parties that you usually would, because we’re just starting to get this under control in this country,” Dr. Bergstrom said.

Dr. Bergstrom said he was also concerned about the more than 20,000 people who are expected to attend the game in person at Raymond James Stadium in Tampa — about one-third of the stadium’s usual capacity.

“Any time you get 25,000 people together yelling and screaming during a pandemic, you’re going to have transmission,” Dr. Bergstrom said.

Public health experts worry that new, more contagious variants, like one first identified in Britain and known as B.1.1.7, will soon become dominant and drive a deadly surge this spring. At least 187 cases of the B.1.1.7 variant have been detected in Florida, more than in any other state, according to the Centers for Disease Control and Prevention.

Bars will be open in Florida during the game, and some are advertising Super Bowl parties. Before the game, Tampa’s mask order was extended to apply to outdoor areas where people could gather.

Super Bowl ticket holders have not been discouraged by the pandemic. Jeremiah Coleman, a Chiefs fan from Wichita, Kan., said, “On my deathbed, this will probably be one of the top five days I remember in my life, you know?”

— Christina Morales and Ron DePasquale The New York Times