As companies in the U.S. look to vaccinate staff en masse, some employers have achieved high rates of vaccination without major mandates -- professional sports leagues.
Several high-profile players have made headlines in recent weeks for not getting the shot, but by and large, the vast majority of their peers have -- at greater rates than the general public.
MORE: NFL preseason kicks off amid COVID vaccine culture warsAround 67% of eligible Americans are fully vaccinated, according to the Centers for Disease Control and Prevention. Meanwhile, leagues such as the NBA, NFL and MLS have rates greater than 90%, with the NHL and WNBA at over 99%.
Some leagues resorted to financial pressure to encourage vaccine uptake. But they also often deployed vaccination campaigns early that relied heavily on education and opportunities for players to connect with trusted medical experts, those involved in the efforts told ABC News.
"As far as the NHL is concerned, this is a very simple and very direct story -- you need to educate everybody as to what good public health practices are when you have a pandemic like this, and where someone who is ill can spread that disease to others at the workplace," Don Fehr, executive director of the National Hockey League Players' Association, told ABC News.
Back in January, months before the recent season started and COVID-19 vaccines were widely available, the WNBA's players' union, WNBPA, started hosting panels with medical experts over Zoom to address players' questions about the pandemic.
"They were curious about everything related to their public health risk, their public health understanding of the pandemic and then specifically about the vaccines," one of the experts on the panel, Jessica Malaty Rivera, an infectious disease epidemiologist and research fellow at Boston Children's Hospital, told ABC News. "They just very earnestly wanted to understand and learn about the stuff that we were sharing."
Malaty Rivera said she has done these virtual "fireside chat sessions" with several companies and teams, from Patagonia to the MLB's Washington Nationals, and finds them to be very effective. In talking with the WNBA players, she and the other medical experts crafted a conversation that touched on how the vaccine approval process works and concerns around pregnancy and fertility.
"They applied what they understood and it shows by the vaccination rates," she said. "We know that it didn't fall on deaf ears."
Leagues including MLS and the NHL provided similar opportunities for players to connect with medical experts and ask questions.
For the NBA, an educational campaign was the "crux of our program," Dr. Leroy Sims, senior vice president of medical affairs for the league, told ABC News.
Starting in February, all 30 teams watched a 20-minute PowerPoint on vaccinations, and the NBA and its players' association made doctors and scientists available to talk with players as a team and one-on-one if desired. Sims often fielded questions on how the vaccines were developed and approved, the impact on performance and side effects.
"It was a really big effort, but it was the most appropriate thing to do -- for us to take that time with our players and our coaches," said Sims, who noted they did similar sessions with players' families, the National Retired Players Association and the league's referees. "No question was out of bounds."
MORE: Majority of companies plan to have COVID-19 vaccine mandate, survey findsWho was delivering that message was also important, Sims and Malaty Rivera said.
"The thing that allowed us to achieve the numbers that we have achieved, in part, is the relationship. The doctor-patient relationship is dynamic, it's engaging, it's a two-way street," said Sims, who is a former team physician and was with the players in last season's "bubble." "It's built on trust."
The panels for WNBA players featured female scientists who are women of color -- which Malaty Rivera said was also "meaningful" for the league's athletes, who are predominantly women of color.
"When you talk about science communication you have to think about the message, the messenger and who's receiving the message," she said.
Some leagues have required staff in close contact with players to be vaccinated. The athletes have yet to face similar mandates, though there have oftentimes been strong incentives to get the shot.
In the NFL, for instance, teams could face potential forfeits and lost paychecks for outbreaks among unvaccinated players. As of July 22, when the policy was announced, 75% of players were partially vaccinated. As of Oct. 7, a month into the regular season, 93.3% of NFL players were vaccinated, the league said.
Unvaccinated players in the NHL and NBA, which both kicked off their seasons this month, could also face docked pay if they are unable to play due to local COVID-19 regulations. Around 96% of NBA players have been vaccinated, with that number expected to climb, league Commissioner Adam Silver said this week. Still, a vocal minority has made headlines for not getting the shot, notably Brooklyn Nets point guard Kyrie Irving. The decision makes him ineligible to play any home games at the Barclays Center, which under New York City regulations requires proof of vaccination for entry, and could potentially cost him millions of dollars.
The Nets decided to bench him entirely unless he gets vaccinated. He has not been allowed to practice with the team and did not play in the team's season opener Tuesday night in Milwaukee.
"It's not always about the money. It's about choosing what's best for you," Irving said during an Instagram Live last week, according to The Associated Press.
Beyond the threat of financial losses, unvaccinated players may have to follow stricter COVID-19 protocols, such as more frequent testing and stricter masking and social distancing measures.
MORE: NBA tells unvaccinated players they won't get paid for missed gamesMLB relaxed some protocols for teams with at least 85% of players and coaches vaccinated; just a handful of the league's 30 teams failed to reach that threshold by the end of the regular season earlier this month.
Unvaccinated MLS players have a different set of COVID-19 protocols, including more frequent testing, and are not allowed to engage in any "high-risk behaviors," such as attending concerts indoors, Johnny Andris, deputy general counsel for the MLS Players Association, told ABC News. Over 95% of players are vaccinated.
"There were enough carrots involved such that the sticks weren't really needed," Andris said.
Other factors may have also helped boost vaccination rates among professional athletes.
MLS players were "very eager to get vaccinated," particularly after the pandemic disrupted the previous season, Andris said.
"MLS was just two or three weeks into the season before things shut down," he said. "The players went right into the 'bubble' tournament down in Orlando, played the rest of the season after that under these really strict protocols. ... I think that whole experience made guys want to get back to normal as soon as possible."
This year's season, which began in April, has seen breakthrough cases, as was expected, though teams haven't had to cancel or postpone games due to an outbreak, Andris said.
The realities of the job -- from frequent travel to close contact with other players while maskless -- may have also helped spur vaccination, NHLPA head Fehr said.
"In normal workplaces, you can engage in a number of practices. You can work remotely. You can wear masks. You can socially distance at the office, etc., etc.," he said. "You can't do that on the ice."
Athletes may have also embraced their standing as role models in getting the vaccine. The WNBA, which wrapped its postseason earlier this week, did a COVID-19 vaccine public service announcement with four players in April, partnered with the Black Women's Health Imperative to support their vaccination efforts and, like other leagues, held community vaccination sites ahead of the 2021 season.
"We saw our role together with the WNBPA as providing players with the best possible information about the vaccine, and I'm proud of and commend the players for their leadership in getting the vaccine while also serving as role models," WNBA Commissioner Cathy Engelbert said in a statement to ABC News.
Silver, the NBA commissioner, told reporters this week he would like to see all players vaccinated in part because they have an "outsized influence on the rest of the public."
"I think it's a public service of sorts," he said, "particularly to young people who might not see the value of getting vaccinated."