State health officials on Thursday issued a stark warning about COVID-19, saying Utah is seeing a surge of cases and that hospitalizations and new cases are at their highest marks since before vaccines were widely available.

“We’re clearly in the middle of a spike in cases and it’s really sad to see and entirely avoidable,” said Michelle Hoffman, deputy director of the Utah Department of Health, speaking at a monthly COVID briefing. “It’s no secret who’s driving this surge in cases and hospitalizations. It’s unvaccinated people. As the governor shared in his remarks, almost everyone who tests positive that ends up hospitalized or even passes away has one thing in common: They are unvaccinated.”

Summit County, however, has the highest vaccination rate in the state, and the county’s health director said there is not a surge in local cases.

“Our numbers still look good. … It’s nothing compared to where we were months ago,” said Rich Bullough, Summit County health director.

He said increasing case numbers in the county have largely been driven by outbreaks contained within families.

But he said what is concerning is the number of so-called breakthrough cases occurring in people who have been vaccinated against COVID-19.

There had been 28 such cases in the county through Thursday, Bullough said, a rate that increased in June.

The county has about 28,000 fully vaccinated people, he said, meaning breakthrough cases happen in about one out of every 1,000 vaccinated people.

Generally, Bullough said, people who contract COVID-19 who have been vaccinated do not get as sick as unvaccinated people, but he said the illness can still be severe in breakthrough cases.

One of the chief concerns, he said, is that the virus that causes COVID-19 will mutate to a form that can elude the vaccines. Already, Bullough said, the so-called Delta variant has made vaccines about 75% effective, down from efficacy rates in the mid-90% range against other forms of the virus.

Officials hope that with vaccine rates of 70% to 90%, populations can achieve herd immunity and severely reduce the virus’ ability to mutate and spread between people. But that has proved hard to achieve.

“We’re going to have variants spinning out of those places that have uncontrolled outbreaks,” Bullough said. “That’s exactly what we’ve seen with the Delta variant coming out of India.”

According to state data, 77% of Summit County residents 12 years or older are fully vaccinated, while 87% of people in that population have received at least one dose of a vaccine.

In neighboring Wasatch County, those numbers are 52% and 57% respectively, roughly in line with numbers in Utah, Morgan and Weber counties.

With the busy July 4 holiday approaching, state leaders on Thursday urged Utahns to seek vaccines.

“What I’m here to say is that 95% of you don’t have to die and 95% of you don’t have to be hospitalized and go through that incredible pain,” said Gov. Spencer Cox. “I can’t tell you how demoralizing it is for our frontline healthcare workers and for families, for everyone.”

Cox was joined by Kencee Graves, the chief medical officer for inpatient services at University of Utah Health, who described the challenges facing healthcare workers.

She said the hospitals are full with people who delayed treatment during the pandemic and that she expected increased hospital visits entering what she called the highest trauma weekend of the year.

“We cannot respond like we did in 2020,” she said, adding that many hospitals are struggling to hire staff.

Graves said she would continue to wear a mask while indoors because of the threat posed by the Delta variant, which she said is 60% more transmissible than previous variants. The earlier variants were themselves 60% more transmissible than the original virus.

Bullough advised people to revisit the prevention techniques used in the early days of the pandemic, when the focus was on physical distancing.

“I think it’s wise to, first of all, be outdoors, be someplace that’s ventilated,” he said. “If you’re willing to wear a mask, wear a mask. If you’re not, try your best to be socially distanced, avoid high-density groups, keep moving.”

He reiterated advice to not be in close contact with others for more than 15 minutes.

“We’re not out of the woods yet,” he said.