Toward the end of his final preseason news conference on Wednesday — after he'd finished discussing the knee surgery for his up-and-coming tight end that capped an exhibition season in which he'd tried harder than ever to keep starters healthy — coach Mike Zimmer was asked to reflect on all the turmoil he'd seen in his time with the Vikings.

"I think it's been eight years," Zimmer said. "Yeah, it seems like the book is going to be a good book, when I write it."

He listed his kidney stones in 2014, his 2016 eye surgery, Adrian Peterson, and then added, "There's a lot that you guys don't know. I'd have to go get all my notes. But you know what? It's like that at probably every place. Everybody has their trials and tribulations, I guess.

"It depended on the place. I was in a place [Atlanta in 2007] where the coach [Bobby Petrino] quit three-quarters through the year."

Then, Zimmer cracked, "Maybe it's me, now that I think about it."

His eighth season as Vikings head coach will begin Sept. 12 in Cincinnati, where he worked for six years as Bengals defensive coordinator and near where he still spends his offseasons at his ranch in northern Kentucky. The team he takes to Paul Brown Stadium seems well-supplied with two things: high-level playmakers who could engineer the Vikings' fourth playoff trip in eight years, and uncertainty that could send the season careening off course.

After finishing 7-9 in 2020, the Vikings scrapped a plan to retool the defense with young players, adding veterans like Dalvin Tomlinson, Patrick Peterson, Xavier Woods, Mackensie Alexander and Bashaud Breeland to a group that finished 29th in the league last year after five seasons of top-10 rankings. The Vikings reworked Anthony Barr's contract to help pay for it all, smoothed over a contract dispute with Danielle Hunter as he returned from a neck injury and picked Virginia Tech's Christian Darrisaw in the first round with plans to play him immediately at left tackle.

But they began training camp by shifting offensive line coach Rick Dennison to a different role once his refusal to get the COVID-19 vaccine made him ineligible, under NFL protocol, to work on-field with players. Vikings players were vaccinated at a lower rate than any team in the league through much of camp, triggering an internal debate over vaccine hesitancy that reached its peak when rookie Kellen Mond's positive test left Jake Browning — the team's only vaccinated quarterback — as the only one able to practice.

Darrisaw didn't practice in camp, traveling to Philadelphia in mid-August for his second groin surgery of the year; Justin Jefferson missed a week with a sprained AC shoulder joint; Barr was rarely seen while trying to manage knee issues; the offense managed two preseason touchdowns; and the Vikings lost three returning skill players — Bisi Johnson, Chad Beebe and Irv Smith Jr. — to injured reserve.

Through the coach's time in Minnesota, the Vikings' seasons have generally followed a pattern. Even-numbered years have been marked with chaotic moments like Peterson's suspension in 2014 or Teddy Bridgewater's knee injury in 2016; the Vikings have enjoyed more tranquility during the odd-numbered years (2015, 2017 and 2019), which all ended in the playoffs.

The 2021 season — one in which the stakes are high for Zimmer, general manager Rick Spielman, Cousins, Hunter, Barr and eight other starters who could hit free agency this spring — could follow the Vikings' odd-year playoff pattern, or it could bring an oddly familiar dose of even-year strife.

Any of it, for these Vikings, seems within the realm of possibility.

"On all sides of the ball, I feel like we are going to be pretty good," Zimmer said after the final preseason game, "but you still have to go out there and prove it."

The Vikings and the vaccine

If the Vikings' season feels as if it's on a tipping point, perhaps it's because of how much their chances are subject to star players' availability. That's true of most NFL teams in most seasons, but in addition to injury, the Vikings remain uniquely vulnerable to losing players to the league's COVID-19 protocols because of how many players are unvaccinated.

Of the 69 players on the Vikings' current active roster or practice squad, at least 13 are either unvaccinated or not yet fully vaccinated, according to Star Tribune observations throughout training camp (unvaccinated players must wear masks and wristbands in certain situations), players' own public comments and multiple team and league sources. The list includes 12 of the 53 players on the team's active roster, and five starters: Kirk Cousins, Dalvin Cook, Adam Thielen, Dalvin Tomlinson and Harrison Smith.

The Washington Post and NFL Media reported Friday the leaguewide vaccination rate remains at 93% after final roster cuts. The Vikings' rate is, at best, 81.2% among players on the active roster or practice squad, though a source with knowledge of the situation said several players are in the process of getting vaccinated.

The Vikings' status as one of the league's least-vaccinated teams has irked Zimmer, who has delivered public calls for vaccination and sounded exasperated by unvaccinated players throughout camp. Behind the scenes, the issue has stirred tension in the organization; unvaccinated players have been met with frequent pressure from key decisionmakers to get the vaccine, sources said.

After his time on the COVID-19 reserve list in early August made him a lightning rod for public and private criticism, Cousins returned on Aug. 5 and opened his news conference by saying the Vikings had put quarterbacks in too small a meeting room, which made him a close contact of Mond (who was also unvaccinated and had tested positive). Cousins refuted Zimmer's criticism from a KFAN radio interview the day before, saying "I very much believe in the protocols" and adding he'd considered measures as stark as holding position meetings outdoors in January or surrounding himself in Plexiglas. He called his vaccine status a personal decision and has chosen to keep it private.

Under current NFL COVID-19 protocols, unvaccinated players who test positive miss at least 10 days, and unvaccinated or partially vaccinated players deemed a "high-risk" close contact with a COVID-positive individual must quarantine and test negative for five consecutive days. Fully vaccinated players are required only to quarantine because of a positive test, not because of high-risk close contacts.

The VIkings parted with their vaccinated quarterback, Browning, after an erratic preseason and brought back Sean Mannion once Seattle released him, giving themselves a veteran if Cousins were unavailable at some point this season.

But quarterback is hardly the only position where the Vikings could be vulnerable. They have at least two players who are not fully vaccinated in four other position groups: running back, wide receiver, defensive tackle and defensive back.

Being more cautious

The Vikings also begin the year tied with the Cowboys for the most players in the league on injured reserve (11, according to Over the Cap) and find themselves short on depth in some spots because of a roster that again has more players with eight-figure average salaries than most of the league (the Vikings are currently tied for fourth with eight players averaging at least $10 million a year).

Following a year when the Vikings lost Hunter in training camp and Barr to a torn pectoral muscle in Week 2, Zimmer shifted his preseason approach, sitting more than 30 starters in the first preseason game and limiting the starting offense to six series in the next two games while holding Cook and Jefferson out the entire time. He lost Irv Smith to a knee injury in the preseason finale anyway.

"I get upset when things don't go the right way, but we've just got to do our best to keep these guys healthy," he said. "Back when I first got here, we were hitting every day and just trying to develop the mentality of this football team and this organization. I think I have that now here, so I probably don't have to go out here and scrimmage in pads every single day. But it's also because of the possibility of when you lose a guy like Hunter last year and you lose a guy like Irv Smith this year, you're going to be a little bit more cautious I think in some of those things that you do."

He added: "If we get the wrong guys hurt, we are going to struggle in a lot of ways."

The loss of players like Irv Smith aside, a fully intact Vikings roster seems talented enough to make the playoffs, especially if new offensive coordinator Klint Kubiak finds his rhythm as a play-caller and the reworked defense approaches the standard set by the 2015-19 groups.

Anything short of that could trigger major offseason changes. Cousins carries only a $10 million cap charge if traded after 2021, Barr's contract voids after this season and Hunter has an $18 million roster bonus due in March, while Zimmer and Spielman's deals run only through 2023.

Their 2020 season crumbled with inexperienced defenders at the mercy of veteran QBs like Aaron Rodgers operating in empty stadiums; the 2021 Vikings are banking on fully developed veterans and full-throated crowds at U.S. Bank Stadium to turn another odd-numbered year into a postseason trip.

If Zimmer ever does sit down to write the book he muses about from time to time, this season could make for a scintillating chapter.

"If anything, you kind of expect change to happen so you're not caught off guard when it does," Cousins said. "But a big part of lasting in this league and having success consistently is finding a way to be resilient and still produce no matter what may change in your environment."