State health and education officials are reviewing a new federal mask-wearing recommendation for all people, regardless of vaccination status, in K-12 schools and counties with high or substantial levels of viral transmission.

The guidance issued by the Centers for Disease Control and Prevention on Tuesday was in response to a COVID-19 wave fueled by the delta variant of the coronavirus that has caused widespread infections in other states and appears to be emerging in Minnesota.

Fourteen Minnesota counties had infection rates Tuesday that were high enough to trigger the federal mask recommendation, including Scott County in the Twin Cities area. The other 13 are smaller counties with rates that can fluctuate widely from week to week.

Exactly how the guidance will be implemented in Minnesota is unclear, but a joint statement by the state departments of health and education said, "We will be using the updated CDC guidance to inform our state guidance, including our school guidance coming out in the near future."

Pandemic activity bottomed out in Minnesota in late June — with Tuesday's federal COVID-19 profile listing the state with the eighth lowest rate of new cases — but has since increased along with the prevalence of the more infectious delta variant.

The 168 COVID-19 hospitalizations reported on Tuesday by Minnesota health authorities was an increase from 90 on July 14.

The positivity rate of COVID-19 diagnostic testing also rose to 2.7% — below the state's 5% caution threshold but above a recent low of 1.1%.

The CDC guidance is based on the seven-day rate of new infections — with masks recommended among vaccinated and unvaccinated people in counties with rates of 50 infections per 100,000 people or higher. Lake, Lake of the Woods, Redwood, Wilkin, Cottonwood, Dodge, Isanti, Mille Lacs, Pope, Roseau, Swift, Traverse and Waseca counties also have rates above this threshold.

The recommendation might not be welcome news to people who enjoyed a reprieve from masks this summer, but Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, said it provides extra protection against a COVID-19 wave that could have been avoided with broader vaccination.

Walensky added that breakthrough infections in vaccinated people remain rare but appear more common when the delta variant is involved.

Minneapolis Health Commissioner Gretchen Musicant said she will "look closely" at the CDC guidance to inform ongoing discussions about the city's pandemic response.

Many school districts already were discussing mask requirements following a recommendation from the American Academy of Pediatrics.

The Rochester school board is slated to consider a mandate for students younger than 12 who have no access to vaccine and a mask-wearing recommendation for others.

People might be tired of masks, but the new recommendation is a protective step to reduce transmission of the delta variant among unvaccinated and even vaccinated people, said Louis Mansky, director of the University of Minnesota's Institute for Molecular Virology. It also buys time for hesitant people to get their shots.

"I think it's a much more conservative stance and a more protective stance," he said. "Is that going to go over very well in the public? Probably not. Even scientists are a little exhausted."

State health officials said a slowdown in COVID-19 vaccinations created opportunities for the more infectious variant to take hold in Minnesota, where more than 3.1 million people — or 66.7% of the 12 and older population — have received at least first doses.

Minnesota at one point was on pace to reach its goal of providing vaccine to 70% of people 16 and older by July 1.

Now, state officials project Minnesota will hit that incremental target by the end of August.

Gov. Tim Walz withdrew Minnesota's mask mandate for indoor public spaces on May 13 — one day after the CDC lifted its prior recommendation for vaccinated people to wear face coverings — at a time when pandemic and vaccination trends were favorable.

Mayo Clinic 14-day forecasting at the time showed a continued decline in COVID-19 rates in Minnesota, but that same modeling now shows an increase in the state's infection rate over the next two weeks.

The state on Tuesday reported three more COVID-19 deaths and 1,032 more infections — accounting for all infections reported over the weekend. The latest figures raised Minnesota's totals in the pandemic to 7,656 deaths and 610,839 infections.

Genomic sequencing of positive specimens in Minnesota suggests that as many as 75% of new infections are caused by the delta variant that was identified in India.

Mansky called the delta variant a "more fit virus" that produces higher viral loads in individuals and "is more efficiently transmitted from one person to another" compared with earlier versions.

Walz, who no longer has the authority of a state emergency order to issue mask mandates and other protective measures, said he would continue to urge vaccination as the primary strategy for Minnesota against COVID-19.

"A year ago, the only vaccine we had against this was social distancing, closing businesses and masking. That is no longer true. We have the vaccine," Walz said at a public event before the CDC announcement. "All of the angst around what is going to happen, what are we going to do with masking, all this, let's just be very clear: We control our destiny 100%" through vaccination.

Walz urged Minnesotans to get their shots, noting an 80% vaccination rate would improve the odds of unrestricted K-12 education and events such as the State Fair. "The State Fair was the brass ring over the last 18 months we were trying to get to," he said, "and we're so close."

Staff writers Glenn Howatt, Erin Golden and Briana Bierschbach contributed to this report.

Jeremy Olson • 612-673-7744@

Correction: A previous version incorrectly described the threshold for federal mark-wearing guidance for counties.