In the months and years following the attack on the World Trade Centre on Sept. 11, 2001, sports fans became used to body searches and metal detectors on their way into arenas and stadiums.

People accepted the measures as a way to keep everyone safe.

After the coronavirus pandemic is conquered and sports re-emerges, it's likely a new layer of security will be introduced.

An Ottawa area doctor has already predicted what one additional level of security might look like.

"It would be effectively barcode enabled," says Dr. Kumanan Wilson, an innovation advisor at Bruyère and a physician at the Ottawa Hospital. "Just like when you go to a sporting event [and] they scan your ticket, they are going to scan your barcode for proof of immunity."

Until there is a vaccine, which appears to be many months away, Wilson says there could be an alternative.

He helped develop CANImmunize, an app that allows Canadians to track their immunization history.

"We're going to need some kind of test that is proof of immunity to get people back into society," Wilson told CBC Sports. "Otherwise, it's a roll of the dice trying to open up these stadiums and large gatherings of people."

A proposal of proof of immunity from CANImmunize that might allow fans to gather in crowds at stadiums and arenas without threat of contagion. (CANImmunize)

Wilson uses a sports analogy to explain how the body builds up immunity.

He describes initial exposure to coronavirus as your body playing another team for the first time. The body may lose the first game, but it learns from the initial encounter and develops a memory and response, which is what antibodies are.

Wilson says using this model is more reliable than doing constant testing, which many leagues are proposing.

"Testing will clear you at that moment in time. The best ongoing proof will be that you have antibodies in your blood."

Wilson says the federal government in Canada and countries around the world need to create a standard definition of what immunity is.

"It can't be a wild west of 'this lab says you are and this lab says you aren't.' You'd have a catastrophe at a sports stadium or at a mass gathering where everybody gets infected again."

Wilson says about half to three quarters of the population would need to develop immunity for the disease to stop spreading.

"Until then, we can't have these mass gatherings. We can have smaller gatherings. We will allow society to go back to normal but in a muted way."

The question is will there be patience for a "muted" return.

WATCH | Trump aims for sports return as soon as possible:

President Donald Trump says he wants fans back in arenas 'as soon as we can'. 0:44

With much of North America under lockdown and deaths in many states continuing to climb, President Donald Trump recently spoke to the commissioners of the NBA, MLB, NHL, NFL and other sports about how the leagues could help "open our country again.

"I want fans back in arenas soon. And the fans want to be back," the president told them.

Nathan Kalman-Lamb is a professor at Duke University who studies the intersection of labour, race and sport. He says the president's comments show that there is a desire to fast track the return of major spectator sports.

"I am very confident that in the major sports leagues, the big four and beyond, we are going to see a return to relative normalcy. And that's probably because sport plays such a pivotal role in our popular culture North America today," Kalman-Lamb said. "Even as we enter dire economic conditions to go along with the dire health condition, I think we're still going to see a real appetite for sport as people look for a form of distraction from the very real traumatic conditions of their lives."

Possible return scenarios

As various leagues plot their next steps, there are a number of key questions and hurdles at seemingly every turn.

The NBA, NHL and MLB have floated the idea of staging games in empty stadiums that are all located in the same geographic area.

For example, the NBA is reportedly exploring the idea of playing a shortened post-season tournament in Las Vegas, with all of the players and team personnel being housed in a nearby village, living under a virtual quarantine.

It would obviously require buy-in from the players and already there is skepticism.

"What is the word 'sport' without 'fan'?" Lebron James, the league's biggest star, said in response to the proposal. "There's no excitement. There's no crying. There's no joy. There's no back-and-forth. There's no rhyme or reason."

WATCH | Sports leagues weighing return options:

Ever since Donald Trump talked to a handful of sports commissioners, plans seem to be leaking about possible return scenarios. Rob Pizzo looks at a few. 2:31

MLB seems to be contemplating a similar idea. One that would see teams living exclusively in Arizona and play their games in stadiums contained within the state.

"I think players are willing to do what's necessary because I think they understand the importance of baseball for their own livelihoods and for the interest of our country and providing a necessary product that gives all the people that are isolated enjoyment," said Scott Boras, one of baseball's most powerful player agents, to the Associated Press.

The NFL maintains it will start its season in September as scheduled with full stadiums of cheering fans. The league's chief medical officer, Dr. Allen Sills, acknowledged that there are many obstacles. Sills told NFL.com that widespread point of care testing, which isn't currently available, would have to be in place and administered often to players and team personnel.

"As long as we're still in a place where when a single individual tests positive for the virus that you have to quarantine every single person who was in contact with them in any shape, form or fashion, then I don't think you can begin to think about reopening a team sport," Sills told the league's website. "Because we're going to have positive cases for a very long time."

Legislative restrictions

Even if leagues persisted in opening up their games to fans, most teams in all four of the major sports play in provinces and states that currently prohibit large gatherings of people. For example in California, home to three NFL teams, Governor Gavin Newsome told reporters there are too many unknowns to even consider a September kickoff, especially one that includes fans.

"I'm not anticipating that happening in this state," he said. "Right now I'm just focusing on the immediate, but that's not something I anticipate happening in the next few months."

Beyond legislative limitations, some officials wonder how willing fans will be to gather in large numbers.

"When we are past the pandemic, I have a hard time believing that once an order is lifted people are just going to flock to go back to 50 or 100 thousand seat stadium like they did before," Amy Hutchausen, Commissioner of the NCAA's America East Conference, told the Wall Street Journal.

Given all of this, the most direct route to an accelerated return without an acceptable level of immunity appears to be sports played purely for television audiences, which would alleviate many of the unknown public health risks.

"They need to put [games] on television and there's going be a huge market for it," Kalman-Lamb points out. "It's fair to say that we will see a return to televised spectator sport before we return to most other institutions that organize our social life."