• New infections have dropped to an average of more than 74,000 per day over the past week, a 57% fall from the delta wave's peak level of 172,500 new cases per day on Sept. 13.
• The downward trajectory has plateaued in recent weeks, bouncing between 70,000 and 75,000 new cases a day for nearly three weeks, according to data compiled by Johns Hopkins University.
• The daily death toll remains elevated, with more than 1,200 fatalities per day reported over the past week, according to Johns Hopkins, up 1% from a week ago.

After weeks of plunging U.S. Covid-19 cases, the decline in infections has stalled out.

New infections have dropped to an average of more than 74,000 per day over the past week, a 57% fall from the delta wave's peak level of 172,500 new cases per day on Sept. 13.

While that surely is good news, the downward trajectory has leveled off in recent weeks, bouncing between 70,000 and 75,000 new cases a day for nearly three weeks, according to data compiled by Johns Hopkins University. Covid hotspots across the U.S., in the meantime, have shifted away from much of the South.

The daily death toll still remains elevated, with more than 1,200 fatalities per day reported over the past week, up 1% from a week ago, according to Johns Hopkins.

Cases have fallen most sharply in the South, where the delta wave hit earliest and hardest over the summer, with average daily infections in the region down by about 84% from peak levels and continuing to fall. The decline has been so steep that Florida, where hospitals were overrun as it fought one of the worst Covid outbreaks in the nation this summer, is now the state with the fewest number of average daily new cases on a population-adjusted basis.

Other Southern states that saw significant delta wave spikes including Georgia, Louisiana and Mississippi also rank in the bottom 10 states measured by daily new cases per capita.

Hospitalizations and deaths are also down in the South. The region's seven-day average of 112 Covid patients per 1 million residents is the lowest in the country, according to a CNBC analysis of data from the Department of Health and Human Services.

"We came from a very high spot, so we had our spike a little bit earlier," Dr. Sonja Rasmussen, a professor in the departments of pediatrics and epidemiology at the University of Florida College of Medicine, said of her state's declining cases. She noted that the cooler fall and winter temperatures in the typically tropic climate make it easier for Floridians to spend time outside, where the virus does not spread as easily as it does indoors.

"I think we are really starting to see some seasonality – maybe not winter-spring like we see with the flu, but more when people are more indoors versus outdoors," she said. "In Florida, we were more indoors in the hot time of the summer, and now we have the opportunity to be more outdoors."

Things are trending in the opposite direction outside of the U.S. South. Cases are up 25% in the Midwest, 18% in the Northeast and 4% in the West over the past two weeks. Hospitalizations, which lag reported infections, are down 9% in the Northeast over that same period but largely flat in the Midwest and West.

The Midwest is now the region with the highest rate of daily new cases per capita, with the recent increase driven by states like Nebraska, Minnesota and Wisconsin. Minnesota's current level of cases, an average of about 3,000 per day, is "among the highest we've seen so far in 2021," according to a tweet from the state's health department Tuesday. "Sadly, the pandemic is far from over," the tweet read.

Population-adjusted cases are next highest in the West, where New Mexico, Colorado and Arizona have all seen increases of 15% or greater over the last 14 days.

The University of Colorado's hospital was beyond capacity last week, according to Dr. Jonathan Samet, the dean of the Colorado School of Public Health and leads the state's Covid modeling group, due to a combination of the disease and "all the reasons that people go to hospitals."

"When I talk to my clinical colleagues, things are full, the ERs are packed," Samet said, noting that his system can meet current demand but has very little room to expand beyond that point. Emergency orders from Colorado Gov. Jared Polis allow hospitals to transfer patients to other facilities if needed, he said, "but the hospital reserves or the beds are at a lower point than during our big surge a year ago."

Polis issued an executive order on Oct. 31 allowing the state's Department of Public Health and Environment to require that hospitals at or near capacity stop new admissions and transfer patients to other medical centers. State health officials also can now order hospitals to accept patient transfers.

About 85% of staffed intensive care unit beds are being utilized statewide in Colorado, according to HHS data, seventh highest among all states. Roughly 36% of those beds are being used for Covid patients, which ranks fourth. 

Samet said a combination of colder weather and low vaccination rates in parts of the state were helping to drive the recent flare-up.

"Like many states, vaccination's a patchwork," he said. "Our rural areas tend to have lower vaccination rates, and right now, they have the highest case and hospitalization rates." 

Samet couldn't put his finger, though, on why Colorado was going through a particularly bad Covid spike relative to other states. Population-adjusted cases are nearly twice as high in Colorado as they are in neighboring Kansas, though other adjacent states like Wyoming, Utah and New Mexico also have unusually bad outbreaks.

"The unvaccinated are the drivers as in many other places, but, you know, we're not different from other states in having a substantial proportion of people who are still unvaccinated and are propagating the epidemic," Samet said. "We know that the unvaccinated are critical, but that doesn't lead us to why Colorado in this particular moment."

Rasmussen, the University of Florida doctor, also mentioned low vaccination rates as reasons to believe that Florida and nearby states like Mississippi, Louisiana and Alabama are still at risk for future outbreaks — despite any immunity residents have built up from the summer delta surge.

"Their vaccination rates are not high enough to make me feel comfortable that we're not going to see continued outbreaks when people get together, in particular in areas where the vaccination rates are lower," she said.

Florida's 60.2% of fully vaccinated residents is a couple percentage points higher than the country's overall rate, though Rasmussen mentioned that there are many pockets of counties with lower rates. Alabama, Mississippi and Louisiana are all in the bottom 10 states ranked by complete vaccination rates, at 45.2%, 46.2% and 48%, respectively, according to the Centers for Disease Control and Prevention.

Further progress in treatments and vaccinations may help Covid transition into what experts call an "endemic" virus, meaning that it is not totally eradicated but becomes more manageable and part of the respiratory viruses that the country deals with on a yearly basis.

The emergence of new antiviral Covid pills from Merck and Pfizer, for example, could help prevent infections from resulting in hospitalizations or deaths. Pfizer's new treatment is no replacement for vaccinations, Dr. Scott Gottlieb, a Pfizer board member and former FDA commissioner, told CNBC's "Squawk Box" on Friday, but it could offer a greater degree of protection for individuals at risk for severe Covid complications.

"When you have therapeutics that are this effective, that can be a backstop for people for whom vaccines don't work, people who have breakthrough infections – there's pills being studied in that setting," Gottlieb said. "It really is a backstop against death and disease from this infection."

Pfizer released data Friday on a Covid pill that cut the risks of hospitalization and death by 89% in high-risk adults, pairing the drug with an HIV medication to keep it working longer in the body. Merck and Ridgeback Therapeutics said in October that their antiviral lowered the chances for hospitalization and death by 50% in patients with mild or moderate Covid cases.

U.S. vaccination rates may also get a boost with the start of President Joe Biden's workplace vaccine mandates, enforced by the Occupational Safety and Health Administration. All businesses with at least 100 employees must ensure their personnel are fully immunized against Covid by Jan. 4, and any employee who refuses to comply must wear a mask and get tested regularly.

OSHA's mandate will affect some 84 million private sector workers, though the new rules are already facing resistance in court.

Covid vaccines were also recently approved for children ages 5 to 11. CDC Director Dr. Rochelle Walensky authorized Pfizer's vaccine last week, clearing the way for shots to go into younger kids' arms.