On Tuesday, the 644th day of the COVID-19 pandemic, nearly two years after it began ravaging American life, more than 100 players in the nation’s two biggest sports leagues were sidelined by the virus.

Thirty-six NFL players tested positive on Monday. Dozens more joined them Tuesday, including eight Cleveland Browns. In the NBA, meanwhile, 10 Chicago Bulls and seven Brooklyn Nets are in the league’s health and safety protocols. Practices are being canceled. Team facilities are being closed. Enhanced protocols are being considered. The NBA, NHL and English Premier League have postponed games this week. Some executives reportedly feel that the worst is yet to come.

It’s not quite clear why the virus has suddenly swept through multiple sports leagues on multiple continents. U.S. case counts are relatively high, but still below previous peaks. There are theories among experts and non-experts — The Omicron variant? Thanksgiving gatherings? Waning vaccine protection? — but they all dodge the elephant in the room, the exasperated question that fatigued fans can’t help but ask:

Why, 21 months into the pandemic, with vaccines widely available, is COVID-19 shelving more players than it did pre-vaccine, or ever before?

The answer is that leagues aren’t testing enough. Or it’s that they’re testing too much.

It’s that leagues have relaxed protocols and decreased testing frequency, allowing isolated cases to turn into clusters. Or it’s that they continue to test young, healthy, asymptomatic, vaccinated athletes, which they have little reason to do anymore.

Those contrasting views have bubbled up again as the virus has spread through locker rooms this month. The first view is the conventional one that most medical experts would espouse. The second is the provocative one: Why can’t athletes play through mild cases of COVID-19? Why are leagues still testing players at all?

“It’s a really, really good question, and one I've struggled with myself,” Zach Binney, a sports epidemiologist at Oxford College of Emory University, said Tuesday. “When do we stop?”

The most definitive conclusion he came to in a 25-minute interview wasn’t that either view was categorically right or wrong. It was that the NFL’s current approach — a middle ground between the two extremes — probably isn’t logical right now.

“If you're gonna do it, do it,” he said of testing and mitigating COVID-19 spread. “If you're not, don't. Take the PR hit — because you know some people aren't gonna like it — but move on.”

Sports sets an example

Binney, to be clear, doesn’t think sports leagues should move on. Certainly not right now, with multiple high-risk variants spreading, and hospitals filling, and overall COVID prevalence high. The leagues, he and others have said, still have a responsibility to protect both their players and their communities. Beyond vaccination, surveillance testing remains their next-best form of defense.

To ditch testing, and accept the probability that COVID would spread unchecked through some locker rooms, the NFL or NBA would need to get their respective players associations on board. They’d need players to accept increased risk to themselves and everybody around them, a risk that some would balk at.

On the first aspect of it, Cameron Wolfe, a Duke infectious disease professor who has advised major sports organizations, pointed out: “We still get a small percentage of athletes who develop long-COVID symptoms. I don't think we understand enough about what vaccination does to that risk to be flippant about it.”

On the second, Binney noted: “Any case that occurs through spread on a team is a case that could continue to spread into the community and make other people sick.”

On a micro level, players likely wouldn’t want to heap that risk onto family members. On a macro level, Binney laid out the counterargument: NFL testing doesn’t have an “appreciable” impact on public health. So why, if the CDC says that “vaccinated people can … refrain from routine screening testing if they have no symptoms or known exposure,” should the NFL continue? Why should NFL teams be seen as responsible for snuffing out COVID transmission if bigger businesses with more employees aren’t?

The answer, Binney said, is that those other businesses should be taking responsibility. “Ideally, every workplace would be acting the way sports teams are,” he said. “Most of them aren't, because they don't have the resources and they don't have the scrutiny.” But their shirking of responsibility isn’t a reason for sports to follow their lead.

In fact, that public scrutiny that sports attract translates to responsibility. “I'm still a firm believer in the positive image professional and college sports can project to the general community,” Wolfe said. “It’s been immensely impactful for college and pro leagues to be able to project how well they have taken up vaccines, for example. If they were to throw caution to the wind and say, ‘Hey we're going to treat this just like a typical flu,’ then I really think that has hugely negative impacts on the standards it sets for the viewing public, who will follow what they see as an example.”

Binney believes there will come a time when leagues do learn to “live with the virus,” and treat it more like the flu, and eliminate testing, and avoid disruptions. But for now, he argued: “If you want to avoid disruption, daily testing is actually better.”

The case for enhanced protocols

The NFL, NBA and almost every major sports league entered their second full pandemic seasons with relaxed COVID countermeasures. The NFL’s plan, which includes weekly testing for vaccinated individuals rather than daily testing, was widely seen as a happy medium between the two extremes. Aside from incentivizing vaccination, it allowed teams to, on one hand, continue to detect the virus while, on the other hand, not worrying about losing players to asymptomatic positives the day before a game.

But those benefits were superficial. There is little upside to weekly testing versus daily testing, beyond the possibility that late detection could marginally reduce the amount of time a player spends sidelined. More importantly, late detection — an inevitable consequence of decreased testing — creates opportunities for a player to spread the virus to teammates.

The clusters of cases within certain NFL, NBA, NHL and EPL teams suggest that intra-team spread is happening, Binney said. The NFL’s weekly testing, often conducted on Mondays, can allow players to play while COVID-positive. But for every missed game they avoid, they’re able to inflict more missed games on teammates. This is how cases multiply. This is how reserve/COVID lists fill and rosters get thin.

This is precisely why the NFL, NBA and others implemented daily testing last year, and why, given the current state of the virus, Binney thinks it might make sense to re-take that step.

Teams battling outbreaks, such as the Browns, have adopted the NFL’s “enhanced protocols.” They’ve held meetings virtually and masked up indoors. But that’s a reactionary step. It won’t get players off the COVID list. The question is whether, as an NFL executive reportedly suggested Tuesday, all teams could adopt the enhanced protocols as a precautionary step. Or whether leagues will realize that, if they want to avoid losing critical players to COVID, weekly testing isn’t sufficient.

‘It’s still a pandemic’

At some point, there will be an alternate solution: Scrap the testing, let the players play. Binney doesn’t know when that point will arrive. He fears that its arrival won’t be a “rational decision,” but rather one made based on “feel,” based on: “When do we feel like society will let us get away with not testing?”

He hopes, on the other hand, that it will be based on data — that leagues will set clearly-defined thresholds, and decide that, once case rates and hospitalizations fall below those thresholds, the testing can stop, at least temporarily, until the numbers rise again. And several factors could raise that threshold, including, as Wolfe said, the “widespread availability of good oral treatments” for COVID-19.

“But for the time being, we're just not there yet, so these interruptions that we see are sadly going to keep happening, as they are with every other element of our society,” Wolfe said.

Then he concluded: “It’s still a pandemic.”

Yahoo Sports’ Jeff Eisenberg contributed reporting.