With twice daily coronavirus tests for players, coaches and staff, a record low number of in-person spectators and a socially distanced halftime show, Super Bowl LV — a matchup between the Tampa Bay Buccaneers and the Kansas City Chiefs to be held in Tampa, Fla. — will look different from years past.

And as Super Bowl Sunday approaches, there are reasons to be hopeful: Two highly effective Covid-19 vaccines are rolling out around the United States and cases and hospitalizations have dropped nationwide.

But cases remain at levels that are nearly twice as high as last summer’s peak and contagious new variants circle the globe, some of which appear to make the vaccines less effective.

Ahead of the big game, public health experts and elected officials are cautioning fans nationwide against hosting large parties that could turn into superspreader events.

Dr. Anthony S. Fauci, the nation’s top infectious disease expert and President Biden’s chief medical adviser for Covid-19, urged people to keep Super Bowl celebrations to a minimum by watching the game at home. On NBC’s “Today” on Wednesday, he pointed to coronavirus spikes that followed celebrations and holidays like Christmas and New Year’s.

“You don’t want parties with people that you haven’t had much contact with,” Dr. Fauci said on ABC’s “Good Morning America” on Wednesday. “You just don’t know if they’re infected so as difficult as that is, at least this time around, just lay low and cool it.”

The Centers for Disease Control and Prevention recommended hosting a virtual Super Bowl party, or an outdoor gathering where guests can spread six feet apart — but even outdoors it’s still important to wear masks the entire time (except when eating).

The C.D.C. also said to try to avoid shouting, cheering loudly or singing, which can increase the amount of respiratory droplets in the air. Instead, clap, stomp your feet or use noisemakers.”

The C.D.C. also said to try to avoid shouting, cheering loudly or singing, which can increase the amount of respiratory droplets in the air. Instead, clap, stomp your feet or use noisemakers. If you attend a gathering, the agency recommends bringing your own food, drinks, plates, cups and utensils.

“This Sunday, remember: Whichever team you’re rooting for and whichever commercial is your favorite, please watch the Super Bowl safely,” Dr. Rochelle Walensky, director of the Centers for Disease Control, said during a White House virus team briefing on Wednesday. “Gathering only virtually or with the people you live with.”

Some states have said restrictions will be loosened in time for the big game. Gov. Philip D. Murphy of New Jersey announced that the 10 p.m. curfew for indoor dining will be lifted starting on Friday. He also raised the ceiling on indoor dining to 35 percent of capacity, up from 25 percent.

In New York City, where indoor dining can resume at 25 percent capacity starting Valentine’s Day, Mayor Bill de Blasio encouraged New Yorkers on Thursday to “not let Super Bowl parties be the reason” the virus keeps spreading.

“If you’re going to do a Super Bowl gathering it should really be just the people immediately in your life,” he said. “The last thing you want to do is get together for the big game and someone gets sick as a result.”

In Florida, the N.F.L. will host fewer than 25,000 fans, a record low, but bars and restaurants remain open throughout the state. Last week, Jane Castor, the mayor of Tampa, signed an executive order requiring masks in certain areas of downtown Tampa and near Raymond James Stadium, the site of this year’s Super Bowl.