After its Aug. 20 headliner Jason Isbell became one of the most outspoken advocates in recent days for stricter COVID-19 guidelines at all concerts, the Blue Ox Music Festival in Eau Claire, Wis., has announced an abrupt policy change requiring proof of vaccine or negative test results during its three-day run next week.

For now, though, most of the other music festivals and big outdoor concerts happening near the Twin Cities in the coming weeks are not implementing stricter policies — even after some of the biggest music festivals around the country announced new rules in reaction to the rising COVID-19 cases fueled by the delta variant.

Representatives from Winstock, Bayfront Blues Fest, the Hella Mega Tour and First Avenue said this week that they do not plan to add any proof-of-vaccine requirements or mask mandates for their upcoming outdoor concerts.

That's in contrast to announcements made by both Milwaukee's Summerfest and Tennessee's Bonnaroo earlier this week that all attendees to their early-September concerts will have to show vaccine cards or negative test results. The New Orleans Jazz & Heritage Festival outright canceled its October plans due to COVID concerns.

In its sixth year, the Blue Ox fest was faced with the chance of losing the biggest name on its lineup card if it did not implement a new plan. Isbell canceled a concert at the Woodlands near Houston scheduled for Wednesday night because he said the venue refused to enforce the new requirements.

"I'm all for freedom, but if you're dead, you don't have any freedoms at all," Isbell told MSNBC on Monday after successfully pulling off vaccine requirements at his Austin, Texas, concert over the weekend.

The change won't be easy for Blue Ox, which attracts a modest festival crowd of around 5,000 fans in a big, open, woodsy campground. Before the announcement was made Tuesday night, co-founder Mark Gehring cited problems sorting through vaccine requirements for staff, volunteers and under-12 attendees at the family-friendly festival.

"And our gates open in seven days, so not a lot of time to disseminate this info," Gehring noted Tuesday.

Still, festival organizers ultimately decided to play it safe, noting in its announcement, "We must all acknowledge that there is still a risk of exposure to COVID-19 at a gathering of people, and by attending, you assume the risk of exposure to the virus."

Returning this weekend to the Duluth harbor for its 32nd year, the Bayfront Blues Festival is counting on its large, wide-open host space and voluntary masking to keep attendees safe while they enjoy Louisiana-reared headliners C.J. Chenier and Tab Benoit. Organizers said they are adding more warning signs about COVID and sanitizer stations and handing out free masks, but they will not require masks or proof of vaccine in the 20,000-capacity venue.

"We have an older demographic that we think is more aware and cautious, and that tends to camp out in their chairs all day already at a safe distance," said the blues fest's production manager, Julia Schroeder.

Organizers of the Water Is Life Festival — happening in Bayfront Park on Aug. 18 with acts including Bon Iver and Hippo Campus — also currently do not plan to add any new COVID-related requirements or rules.

Returning Aug. 20-21 to Winsted, Minn., with headliners Luke Combs and Sam Hunt, the Winstock country music festival is taking a similar approach as the blues fest and encouraging but not requiring distancing and masking. It also is adding extra portable toilets, expanding its check-in points and offering free masks.

Live Nation, which is the promoter behind the Hella Mega Tour with Green Day and Weezer, announced a policy this week leaving it up to individual artists if they want to require proof-of-vaccine or negative test results. So far, Hella Mega's team has not announced any such policy ahead of the Minneapolis date at Target Field on Aug. 23 — even after one of the bands on the tour, Fall Out Boy, canceled a couple of dates last week following a positive COVID test among one of its crew members.

After Live Nation pivoted to requiring a vaccine or negative test results at its Lollapalooza festival in Chicago two weekends ago, president Joe Berchtold said the policy change was "very successfully done."

"Over 90% of the people were fully vaccinated, which I think was a great signal in terms of people's commitment and support of being vaccinated in order to go to these shows," Berchtold said.

First Avenue will host Ween on Aug. 21 outside Surly Brewing Co. without any vaccine or mask requirements in place, just as it did last weekend with Patti Smith — a concert where many fans still masked up voluntarily.

"I really doubt there would be a mask rule for an outdoor show unless it was mandated by the government," said First Avenue's general manager, Nate Kranz.

For indoor shows at its namesake venue and others, though, First Avenue became one of the first big venue operators in the country to begin requiring proof of vaccine or a negative COVID test result for entry starting Aug. 2. Many more venues nationwide are following suit, including a coalition of 11 concert sites in Nashville that announced similar policies Tuesday.