The summer surge of U.S. coronavirus cases has started to ebb after exposing the grave danger the virus still poses in areas where large swaths of the population lack immunity.

A nationwide decline in new infections and hospitalizations is fueled by sharp drops in Southern states that were hit hard by the highly contagious delta variant. Hospital admissions nationwide crested above a weekly average of 100,000 in early September and are still at levels not seen since the winter, before vaccines were widely available. New infections plateaued in the first half of September, averaging above 150,000 daily, and are now on track to slip below 100,000.

But more people infected in the latest surge are expected to die in the days and weeks ahead, with the death toll on the brink of surpassing 700,000 — roughly equivalent to the population of the District of Columbia. The country has already hit the grim milestone of losing 1 in 500 residents to the virus.

In places like Tennessee, Alabama, Mississippi and the Carolinas, the latest wave appears to be following a similar pattern of a sharp spike followed by steep plunge seen in the United Kingdom, India and other places battered by delta. Epidemiologists say this pattern suggests the virus is rapidly burning through pockets of unvaccinated people before hitting a wall.

“In any epidemic wave, you have to have susceptibles,” said David Rubin, who monitors coronavirus trends as director of PolicyLab at the Children’s Hospital of Philadelphia. “Between increasing vaccination and the sheer number of people infected, they likely reached a level where they don’t have any susceptibles left, so the virus is being blocked and it’s one of those disappearing moments.”

Experts including Rubin are now paying attention to states in the North and Upper Midwest that are starting to see cases and hospitalizations creep up, which was expected after schools reopened and people gather indoors with few restrictions as chilly weather returns. Case upticks alone are not cause for alarm if hospitalization spikes do not follow, experts said. Public health leaders have largely accepted the novel coronavirus will never be vanquished, instead turning into an endemic threat such as the flu and other respiratory viruses.

They are also taking stock of the lessons from the summer surge.

As the pandemic reached its worst levels yet in some areas, many Republican leaders have declined to enact mask and vaccine mandates. In Florida and Texas, the GOP governors responded to the surge by blocking efforts to limit the virus’s spread.

Arguments that mask mandates violate an individual’s constitutional right to liberty might not cut it with the Supreme Court. Here's why. (Drea Cornejo/The Washington Post)

Experts caution against declaring steep declines without any interventions to curb transmission as success stories. It’s like suggesting a Category 5 hurricane that barrels through a city in a day is better than a week of heavy rain.

Hospitals across the South and beyond were stretched to their limit and reached all-time highs in admission, taking a toll on exhausted health-care workers. In August, more children were hospitalized than any other stage of the pandemic. Hospitals in Alaska, Idaho and Montana activated crisis standards of care, allowing them to ration health care, one of the worst-case outcomes that had yet to materialize even in the winter wave.

The United States has reported nearly 100,000 new covid fatalities since the summer surge started around the Fourth of July, when President Biden celebrated being “closer than ever to declaring our independence” from covid-19. The nationwide case numbers started to increase soon after.

In Alabama and other states seeing declines in new cases and hospitalizations, experts caution against hasty celebration.

Time and again, people have let their guard down only to see the virus take hold again. And even if that doesn’t happen, the falling numbers fail to reflect the reality of the intensive care unit, where people often stay for weeks.

“The lovely graphs are very reassuring,” said Jeanne Marrazzo, director of infectious diseases at the University of Alabama at Birmingham’s Heersink School of Medicine. “But when you look at toll the ICUs are still bearing, it’s really brutal.”

People linger there, some of them young, and many suffering from complications like blood clots and antibiotic-resistant infections. Meanwhile, doctors and nurses on regular floors are treating patients who would normally be in the ICU.

About 1 percent of Alabama’s ICU beds are available. The Huntsville Hospital Health System is at “negative seven,” according to president and chief operating officer Tracy Doughty, with those seven patients needing ICU care waiting, for now, in the emergency room.

Alabama has the nation’s fourth-lowest vaccination rate, with only 43 percent of the population fully immunized. If those protected people were evenly distributed across the state, they would acts as buffers and the virus would have less chance of taking off. Instead it is ripping through tightknit groups of unvaccinated friends and neighbors who socialize together.

This intensive care unit went down to zero patients with covid-19. But once the delta variant hit, they've seen a return of patients with the virus. (Whitney Shefte/The Washington Post)

“We’ve had families who’ve lost both parents. Multiple siblings. Husbands and wives. Sons and daughters. Parents and children,” said Tracy Luckhardt, a pulmonary critical care doctor at the University of Alabama at Birmingham.

Gov. Kay Ivey (R) called a special session this week for lawmakers to spend federal coronavirus relief dollars, which she and GOP legislative leaders want to spend on new prisons.

Ivey, who criticized unvaccinated people for the spike in July, has since directed her ire at Biden’s plan to compel many employers to require vaccines or regular testing for workers. The state’s health department is still relying largely on a carrot approach for vaccination, deploying faith leaders as messengers and launching testing programs at college football games with a $75 gift card as an incentive to get shots. Ivey’s office did not return a request for comment.

People who contracted coronavirus this summer and the surviving relatives of those who didn’t make it are among the newest foot soldiers in the battle to persuade the remaining vaccine holdouts to get shots.

Days before Waverly, Tenn., police officer Greg Triplett died of complications from covid-19, he sent a heart-wrenching text message to his police chief, telling him to urge people to go get the vaccine.

On the morning of Sept. 24, Triplett wrote: “When I can’t take three steps to sit on a potty chair and feel like a grizzly bear just choked me out, that’s got to be the worst feeling in the world. You’ve got to tell people to get those shots,” his chief, Grant Gillespie, said in an interview.

Just two days later, Triplett, a 50-year-old husband and father of five, died. His final plea inspired at least one officer and a few others who knew him to get their shots, Gillespie said. He said Triplett was unvaccinated.

Cases are plateauing in Tennessee and declining in some areas after averaging above 7,000 new infections per day in mid-September. Experts suspect the virus will continue to smolder in Tennessee throughout the fall and winter, particularly in rural communities such as Waverly, where vaccination rates tend to be low.

“I think that across the country, we will see covid really starting to diminish in a noticeable way, such that we can talk about controlling or staying ahead of this pandemic in a sustained fashion for the first time,” said William Schaffner, an infectious-diseases expert at Vanderbilt University Medical Center. “But I think in states such as my own, we will see covid continue to keep hospitals busy, causing small outbreaks here and there in schools or other places where people gather.”

Pandemic responders hope stories like Triplett’s nudge more people to get vaccinated and prevent future deaths. Tennessee’s death toll passed 15,000 this week.

But political polarization poses a barrier. A Vanderbilt University poll in May found that 94 percent of Democrats surveyed in Tennessee had been vaccinated against covid-19, or planned to be. The corresponding figure among Republicans was 60 percent.

In some cases, the issue is that people don’t want their friends and neighbors who oppose the vaccine to know they want to get the shots.

“There is pressure in these close-knit communities — rural communities as well as urban communities — where people are willing to vaccinate, but in secret,” said Donald Alcendor, an associate professor of microbiology and immunology at Meharry Medical College, a historically Black medical school in Nashville that offers discreet vaccination, including in people’s kitchens.

Infections among children appear to be a driving factor in the nationwide summer wave and are particularly notable in states including Tennessee, which reported more than 75,000 cases in school-age children in August and September.

Pfizer recently submitted data to federal regulators demonstrating its vaccine is safe and effective for children ages 5 to 12, raising the possibility those children can become vaccinated by the end of the year. Widespread childhood vaccination could provide a buffer against future virus waves.

Recent declines can provide some comfort to parents even before the vaccine becomes available to children — but only if adults step up, said Jennifer Nuzzo, an epidemiologist with the Johns Hopkins Bloomberg School of Public Health.

“It’s encouraging news we see pediatric cases falling despite the absence of vaccines because it means we can do a lot by making sure we control spread of the viruses among adults,” said Nuzzo.

Hospitals are also urging Americans to take heed of the summer surge, emphasizing how the delta variant is a different beast, sending young and middle age adults to the hospitals in greater numbers than at any other point of the pandemic.

Officials also warned of the potential for hospitals to face additional strain from a dual threat of rising coronavirus and flu cases this fall. While last year’s flu season was almost nonexistent, experts predict it will return now that people are returning to workplaces and schools. Respiratory therapists and oxygen supplies could be stretched thin.

“All of this points to the need to take every protective step we can for our loved ones and our community in order to make sure we are all safe,” said Nancy Foster, vice president for quality and patient safety policy at the American Hospital Association.

Those risks are weighing on the minds of public health officials in places where covid-19 hospitalizations are creeping up, including in Maine, where admissions are approaching winter peak levels.

Nirav Shah, Maine’s top public health official, says he’s hospitals still have enough ventilators and there are about 50 ICU beds available. But if the system becomes overtaxed with the arrival of flu season and existing routine procedures, there is little leeway to treat more of the unvaccinated, who account for more than 90 percent of the people in ICUs.

Even though two-thirds of eligible Mainers are fully vaccinated, the virus is finding niches in rural areas with smaller rates. Shah cautioned against relying on monoclonal antibodies, a treatment found to keep people out of hospitals, under such conditions.

“If your backup plan is to be in an ICU bed or get monoclonal antibodies, you are miscalculating,” Shah said. “You are doing it wrong.”