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After placing six players on the COVID-19 reserve list on Monday and Tuesday, the Vikings returned to practice on Thursday minus four coaches as a virus that's surged through the NFL this week continued to affect the team.

Senior defensive assistant Paul Guenther has been away from the team with the coronavirus, coach Mike Zimmer said, and the Vikings are also without three strength coaches this week. Head strength and conditioning coach Josh Hingst is still in the building running the weight room, and "then we've had some other helpers come help," Zimmer said.

"I volunteered, but they said they didn't want me," he joked.

The Vikings have placed 16 players on the COVID-19 reserve list since Nov. 4 and had at least five coaches out of the building in that time, as the virus spreads through the league at unprecedented levels. More than 100 players have been placed on the COVID-19 list leaguewide this week.

Browns coach Kevin Stefanski tested positive for the virus for the second time this year, even though he's been vaccinated and received a booster shot. Quarterback Baker Mayfield is among 16 players currently on Cleveland's COVID-19 list.

The Bears, who will play host to the Vikings on Monday night, announced Thursday that offensive coordinator Bill Lazor, defensive coordinator Sean Desai and special teams coordinator Chris Tabor are going through coronavirus protocols.

Minnesota did not place any new players on the COVID-19 list Thursday, but the Bears put six players — including key starters like wide receiver Allen Robinson and safety Eddie Jackson — on the list, while keeping another eight out with what the team described as an illness.

The NFL agreed to revised COVID-19 protocols with the NFL Players Association on Thursday afternoon, immediately requiring masks and social distancing in team facilities regardless of vaccination status, virtual meetings, and restrictions on outside activities through the end of Week 15.

The Vikings had been one of seven teams in enhanced COVID protocols earlier this week; Zimmer said Thursday morning they'd emerged from those protocols, which would indicate they won't have to test vaccinated players every day unless they have more cases or the league agrees to the union's request that all players be tested daily.

The new protocols also allow vaccinated players who tested positive for COVID-19 to return sooner if they are without symptoms. The league had previously allowed vaccinated players to return with two negative tests at least 24 hours apart, but few players had met that threshold given how long the virus can linger in a person's body.

In the new return-to-play protocols, the NFL will test a player's "cycle threshold," which measures the amount of virus still in their system. If a vaccinated player who'd tested positive for the virus is asymptomatic, shows a cycle threshold value of 35 or greater on a PCR test and produces a negative result on a rapid test 24 hours later, the player could return as soon as a day after a positive result.

"Throughout the pandemic we have continuously evolved our protocols to meet our goal of advancing the safety of the players, coaches and staff. The changes we are making today aim to address the increase in cases and the advent of the Omicron variant," the league said in a statement that outlined the changes. "All of these changes are grounded in our data and science-backed approach, with safety our number-one goal for the entire NFL community."

With fans back in the stands this year, the league has resisted rescheduling games, and has yet to cancel a game in the two seasons affected by COVID-19. No matter what happens, Zimmer said Thursday, he's got no doubt the NFL will play every game on its schedule.

"They'll make it," Zimmer said. "They won't cancel any games. I 100 percent for sure believe that."