The NFL is closing in on having 90 percent of its players at least partially vaccinated for the coronavirus at a time when the country as a whole has struggled to reach 70 percent for its adult population. Yet the opening of training camps leaguewide has brought reminders that challenges remain as the sport attempts to navigate its way toward another season during the pandemic.

The NFL’s plans to return to normal for the 2021 season, with stadiums filled with fans and games played on time, have been complicated by the nationwide spread of the delta variant. But the league remains hopeful that its vaccination efforts will allow this season to be played safely and mostly without disruptions.

“All of us certainly are cognizant of what’s going on in society with the delta variant, and we’re monitoring that very carefully,” Allen Sills, the NFL’s chief medical officer, said recently. “We have tailored and adapted our protocols to the threat posed by delta. But we remain convinced, based on medical science and our discussions with public health authorities and other experts, that vaccinations remain our best defense against these variants.”

The league said Thursday that 87.9 percent of its players had received at least one vaccine dose and that 19 of the 32 teams had more than 90 percent of their players vaccinated. That compares favorably to national trends. According to data on the Centers for Disease Control and Prevention website, 69.6 percent of Americans ages 18 and above had received at least one vaccine dose as of Saturday.

“I think we’re off to an excellent start,” Sills said July 23, when the players’ vaccination rate was around 80 percent. “Those numbers are obviously far higher than what we’re seeing in society as a whole. They’re much higher than the demographic of our player population. But we’re, again, not satisfied because we think there’s still work to be done.”

With training camps underway, coronavirus-related issues have persisted. Indianapolis Colts Coach Frank Reich and Baltimore Ravens quarterback Lamar Jackson are among those who have tested positive. The Minnesota Vikings assigned offensive line coach Rick Dennison to a new role as a senior offensive adviser, citing NFL vaccination protocols that prohibit an unvaccinated coach or staffer from working in proximity to players.

“The message that needs to be conveyed to the entire football community is very simple: We are still in a pandemic, and we do need to work together to make it through another complete season,” Cleveland Browns center JC Tretter, the president of the NFL Players Association, wrote on the union’s website. “Given the rise in cases and the emerging data on how the vaccines hold up to the virus’s variants, we should expect the unexpected.”

Pockets of vaccine wariness remain. Buffalo Bills wide receiver Cole Beasley said he’s “not anti- or pro-vax” but “pro-choice.”

“Some people may think that I’m being selfish in making this a ‘me’ thing,” Beasley said, reading from a prepared statement at a news conference. “It is all about the young players who don’t have a voice and are reaching out to me every day because they’re being told if they don’t get vaxxed, they’ll be cut. … Every doctor I’ve gone to with questions begins every sentence with, ‘From what we know now,’ which tells me we don’t know enough.”

Ron Rivera, the Washington Football Team coach who has battled a form of skin cancer, lamented his team’s lagging vaccination rate.

“I’m truly frustrated,” Rivera said. “I’m beyond frustrated. One of the reasons I walked in with a mask on is I’m immune-deficient. … When I’m in a group and the group’s not vaccinated or there’s a mixture, I put the mask on, and I do that for health reasons because nobody really knows [about the delta variant]. I have to do that. And I just wish and I hope that our guys can understand that.”

The NFL and NFLPA developed protocols that ease many restrictions for vaccinated players and staffers. They are tested only once every two weeks, and they’re generally exempt from contact-tracing quarantines, while unvaccinated players and staffers remain subject to daily testing and rigid protocols. That has major competitive implications, which were amplified when the NFL sent a memo to teams saying that if a game is canceled because of an outbreak caused by a team’s unvaccinated players or staffers and cannot be rescheduled, that team will forfeit the game.

“The focus will be on playing 272 games within the 18-week schedule, safely and responsibly,” said Dawn Aponte, the NFL’s chief football administrative officer. “At this point, we do not intend to add a 19th week to accommodate postponements.”

The competitive considerations might give teams incentive to release unvaccinated players when they pare rosters, although league rules say a player cannot be cut based on his vaccination status.

Green Bay Packers General Manager Brian Gutekunst said that in the weeks before training camp, team officials feared they might be facing “a big challenge” on player vaccinations, but they were pleasantly surprised when camp began.

“Our players really started to be educated about what was going to happen and how their daily life here was going to be,” Gutekunst said. “I think that probably, certainly, helped some things. But at the end of the day, it’s personal decisions.”

Sills said he tells patients these are the safest and most effective vaccines he has seen developed during his medical career.

“To me, being vaccinated is not about politics or one’s world view,” Sills said. “It’s simply about being as safe as we possibly can.”