A rise in new coronavirus infections and hospitalizations among the fully vaccinated has altered the COVID-19 picture in Michigan and the United States.

In Michigan, roughly a quarter of 8,100 recent cases have hit those who are fully vaccinated, according to new data released Wednesday.

And while the federal government had said the fully vaccinated accounted for just 3 percent of COVID-19 hospitalizations, the Henry Ford Health System of hospitals said Wednesday that its current rate is between 15 to 20 percent.

Those changes, sparked by the more virulent and contagious Delta variant, prompted the Biden administration on Wednesday to call for everyone to get a booster shot of the vaccines.

While Michigan cases have remained relatively steady for two weeks at about 1,300 a day, Michigan’s top epidemiologist, Sarah Lyon-Callo, told reporters Wednesday that officials fear cases, hospitalizations and deaths could soar to levels seen in Texas and Florida if more people do not get vaccinated and take precautions like mask wearing.

“We could have the same kind of experience here if we don’t make use of mitigation measures,” Lyon-Callo said.

Current projections suggest the state could have another 4,000 COVID-19 deaths in late summer and fall if cases spike, atop the 20,000 since the start of the pandemic last year.

Gov. Gretchen Whitmer’s administration lifted the last major COVID restriction on June 22, and has not ordered new ones amid the steady rise in cases over the past month. She has resisted following the lead of governors in 10 states and issuing a mask mandate for schools, but has strongly recommended that districts require them.

Amid the debate, there have been nearly 2,000 breakthrough cases among the vaccinated in the week ending Aug. 11, out of just over 8,100 total new infections during that same time.

Even though there have been nearly 2,000 "breakthrough cases" in the past week, the rate of infection among the vaccinated is far smaller than those who have not gotten vaccinated. The crude rate, adjusted for population, is 6 daily cases per 100,000 for the vaccinated compared to 17 cases per 100,000 for the unvaccinated.

Public health officials have long said breakthrough cases are inevitable because the vaccines are roughly 90 to 95 percent effective. Recent studies have shown lower rates of effectiveness, especially against the delta variant: with one study from five states found the Pfizer-BioNTech vaccine was only 42 percent effective against that strain.

But medical experts have said those breakthrough cases would likely involve less serious illnesses and deaths.

Physicians from Henry Ford Health Systems, a Detroit-based chain of six hospitals in south and southeast Michigan, said Wednesday that half of the fully vaccinated who have been hospitalized have compromised immune systems.

“We're also seeing breakthrough disease in the very frail elderly, but we are not seeing healthy people who receive the vaccine hospitalized, which again shows you how effective these vaccines are at this time,” said Dr. Dennis Cunningham, the system’s director of infection control and prevention.

From a peak of over 400,000 first doses given in a week in early April, vaccination rates fell quickly, with fewer than 29,000 first doses given in the second week of July.

But the rate of weekly vaccinations has risen since, averaging over 42,000 in the past three weeks. Nearly 65 percent of the population 16 and older have had at least the first dose. At 42,000 first doses a week, it would take over two months to get to Whitmer’s goal of 70 percent.

Those goals could be set back by renewed vaccine skepticism following reports of breakthrough cases. Public health officials said they have seen more people question the vaccine, with some saying “‘See, it doesn’t work,’” said Linda Vail, health officer for Ingham County.

“But it does (work),” Vail said. “It’s highly effective.”

People have routinely gotten boosters for tetanus every 10 years, Vail said, and the use of them does not mean the vaccines have failed.

New data has indicated that the vaccines’ effectiveness wanes over time and in the face of the delta variant which creates a higher “viral load,” making it more contagious.

But Cunnigham said it is not making people sicker.

So far, over 4.7 million Michigan residents have become fully vaccinated and there have been 12,121 documented infections among the vaccinated, or 0.3 percent of the fully vaccinated.

Though vaccinated individuals are a minority of infections and hospitalizations, the increase has prompted calls for booster shots and renewed vigilance — three months after the U.S. Centers for Disease Control and Prevention said it was safe for the vaccinated to stop wearing masks indoors.

In Calhoun County, health officer Eric Pessell, like Vail, has heard more people use the breakthrough cases to question the vaccines.

Of the total 5,900 infections in 2021, 145 were breakthrough cases in the county in 2021, when the vaccines became widely available, about 2.5 percent.

“We just need a lot more people to get their first dose ASAP,” Pessell said.