After falling for weeks, the United States’ COVID-19 case numbers are on the rise again. And unlike the summer surge that hit the Deep South, this time states with some of the nation’s highest vaccination rates are struggling to keep the virus under control. 

As of Tuesday, the U.S. had a seven-day average of 74,584 new reported cases a day, up 17% from Oct. 24, according to data compiled by the Centers for Disease Control and Prevention. Deaths and hospitalizations continue to decline, but those metrics usually lag behind rises in infections.

Twenty-seven states are seeing increases in new cases over the past two weeks — 22 by 10% or more — according to New York Times data. Twenty-three states are reporting decreases.

Alaska has the most per-capita cases at 72 per 100,000 residents, but it is on the downslope of a surge that started this summer. 

Other states currently faring the worst are North Dakota (67 per 100,000), Colorado (65), New Mexico (61) and Minnesota (60). 

Colorado, New Mexico and Minnesota all have vaccination rates over 60%. Even Vermont, which has the country’s highest vaccination rate of 72%, is experiencing a pandemic high in new cases.

Officials and experts in those states point to the same reasons for the surge. They say unvaccinated people are still accounting for the overwhelming majority of hospitalizations and deaths. But they also suggest that waning immunity from vaccines is playing a role.

There’s also the facts that the delta variant is more contagious than previous coronavirus strains, the colder weather is pushing more people into closer quarters indoors and people have changed their behavior when it comes to social distancing and mask wearing, they say.

In Colorado, the Department of Public Health and Environment says COVID-19 is spreading so fast that all adults 18 and older are now eligible for booster shots. 

The CDC recommends people who received the Pfizer and Moderna vaccines get booster shots after six months if they are 65 or older, have underlying health conditions, or live or work in high-risk settings. Colorado officials say almost every adult in the state is now living or working in a high-risk setting. 

Colorado is experiencing its most cases since last December, and its positivity rate is nearing 10%.

UCHealth hospitals said last week that unvaccinated people were accounting for 80% of infections, 78% of hospitalizations and 91% of intensive care treatments.

Colorado Gov. Gov. Jared Polis said the unvaccinated "are putting themselves at risk – which you can certainly argue is their own business, and I have no qualm if they have a death wish. But they’re clogging our hospitals. And I think most Coloradans are sick and tired of trying to protect people who don’t seem to want to protect themselves.”

In Minnesota, the volume of new cases last weekend was so high that there weren’t enough workers to review the data, resulting in a reporting lag, the state Health Department said.

"That's pretty alarming that they couldn't process all the incoming cases," Dr. David Boulware, an infectious disease specialist at the University of Minnesota, told the Star Tribune. "I'm becoming more concerned as our hospitalized cases are this high already preinfluenza and, as the weather turns colder, our cases may likely increase just like last year, further straining the limited number of hospital beds in Minnesota."

Allina Health System in Minnesota said Tuesday about three-quarters of patients hospitalized with COVID-19 and 92% of those in ICUs were unvaccinated. 

In New Mexico, the surge in infections has led to some temporary school closures while stretching hospitals already dealing with a nursing shortage even thinner. 

There, health officials say unvaccinated people made up 72% of new cases, 77% of hospital admissions and roughly 95% of COVID-19 deaths over the past four weeks. 

Vermont escaped the sort of surges other states experienced early in the pandemic. But State Health Commissioner Dr. Mark Levine believes that success might be contributing to the state’s current struggles, despite its high vaccination rate.

Studies estimate that 3% or less of Vermonters developed any immunity to COVID-19 before the delta variant surfaced. The state, which has one of the country’s oldest populations, also was quicker to vaccinate more of its people, meaning it could be experiencing waning vaccine effectiveness sooner, Levine said.

"I know for many of us it can be frustrating to see Vermont looking so different from how we once did during the pandemic, but even after all this time, the virus is not something we have absolute control over," Levine said.

Health officials are still urging more Americans to get vaccinated — an effort being aided by last week’s Food and Drug Administration emergency use authorization of Pfizer’s vaccine for children ages 5 to 11. Meanwhile, Pfizer has requested that the FDA approve booster shots for everyone 18 and over. Boosters have already been cleared after two months for people who received the Johnson & Johnson vaccine.

Most of the states with the fewest per-capita cases now are the same ones that were being battered by the virus this summer, Florida, Louisiana, Mississippi and Alabama among them.

In Louisiana, health officials are cautioning that case numbers have risen and fallen before during the pandemic and the state’s vaccination rate of 48% is not high enough to prevent another surge.

Dr. Jennifer Avegno, head of the New Orleans Health Department, told NOLA.com this week that she believes weather has played a role in the recent decline in cases — milder temperatures are allowing people to spend more time outside, rather than inside in air-conditioning. 

Florida Gov. Ron DeSantis has been using the low case numbers to take a victory lap, saying his hands-off approach to the pandemic — including wars against mask and vaccine mandates — are paying off, while not acknowledging the state's problems this summer.

The Associated Press contributed to this report.