The biggest mystery leading into a March Madness bracket reveal more than a year in the making had little to do with bubble teams or top seeds. Instead, it was the not-so-simple matter of which programs would be healthy enough to play.

Kansas and Virginia, two programs hit with COVID-19 breakouts over the past week, made it into the bracket released Sunday by the NCAA selection committee, signaling both teams believe they’ll have enough healthy players to be ready for their tip-offs next weekend.

That there was any doubt about the Jayhawks and defending champion Cavaliers securing spots in a 68-team tournament that was canceled last year as the COVID-19 virus mushroomed into a worldwide pandemic was the most jarring reminder that the 2021 tournament itself is no sure thing.

All 68 teams will gather in Indiana for all 67 games — no wondering who’s heading West to Boise or who’s going South to Memphis — beginning Thursday and ending April 3 and 5 with the Final Four. But all it takes is a single COVID outbreak to upend the finely calibrated beauty of that plan. More than one and the entire endeavor could crater.

There were no surprises among the four No. 1 seeds. Gonzaga, Baylor, Illinois and Michigan earned those slots - with the Bulldogs the 11-4 favorite to win it all and become the first team since the 1976 Indiana Hoosiers to finish a season undefeated.

The last teams to earn the 37 at-large bids — one more than usual because the Ivy League canceled play this year — were Drake and Wichita State, which play Thursday in a First Four game, and UCLA and Michigan State, two decorated programs with surprisingly low seeds that meet in another play-in game.

But four teams that didn’t make it — Louisville, Colorado State, St. Louis and Mississippi — have been put on stand-by. They could find their way into the bracket if a team in the field notifies the NCAA by Tuesday night that it must withdraw because of health concerns. After that, if a team pulls out, its opponent will advance via what is essentially a forfeit.

Fittingly for such an unpredictable season, some teams hoping to sneak in off the bubble were denied when Oregon State and Georgetown — coached by its own former superstar, Patrick Ewing — won their conference tournaments.