MINNEAPOLIS — Minnesota health officials warned Monday that the highly contagious delta variant of the coronavirus now accounts for more than 75% of the state’s new COVID-19 cases and that it’s a serious threat to people who still have not gotten vaccinated.

“There definitely is a mindset that we’re done with COVID,” Health Commissioner Jan Malcolm said during a briefing for reporters. “But it’s more accurate to say that that we’re in a critical transition phase.”

The commissioner said the state has made important progress and now has much better tools for fighting the pandemic. But she warned that the state has not reached herd immunity, and that vaccination rates in some parts of Minnesota are far below average. The variant will find unprotected people and infect them at much higher rates, she said.

The delta variant has gone from causing less than 1% of Minnesota cases to over three-quarters in just a few weeks, said Kris Ehresmann, the state’s infectious disease director.

Malcolm said unvaccinated Minnesotans make up the vast majority of the state’s new cases and hospitalizations. “Breakthrough cases” among vaccinated Minnesotans remain “very rare,” she said, adding that 99.9% of Minnesotans who are fully vaccinated have not contracted the virus.

Put another way, Ehresmann said, fewer than 3,900 out of nearly 3 million fully vaccinated Minnesotans have had breakthrough cases.

Malcolm said she expects Minnesota will reach vaccinating 70% of its population 16 and older by the end if August, but she called that a milepost, not a goal to settle for.

Malcolm and Ehresmann held the media briefing, their first in several weeks, as the state’s case numbers head back up after a quiet period. While the state’s new case numbers had fallen to around 100 per day several weeks ago, they’ve climbed into the 200s and 300s and even to 400 recently. They said the state is not actively considering vaccination mandates or re-imposing other restrictions, but that they welcome it when employers voluntarily take such steps.

“Our actions are going to help determine what the next phase of the pandemic looks like and how disruptive it will or won’t be,” Malcolm said.