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The coronavirus pandemic in the United States has turned into a patchwork of regional hotspots, with some states hammered by a surge of infections and hospitalizations even as others have seen the crisis begin to ease. The spring wave of the pandemic has driven hospitalizations above 47,000, the highest since March 4.

Thirty-eight states have reported an increase during the past week in the number of people hospitalized with covid-19, the disease caused by the virus, according to a Washington Post analysis of data provided by the Department of Health and Human Services.

But the national statistics don’t capture the intensity of the coronavirus emergency in the hotspots. Michigan reported more than 10,000 new infections on Tuesday alone. The state on Wednesday reported an average of 46 deaths a day, up from 16 a month earlier.

“We’re still climbing, unfortunately,” said Nicholas Gilpin, system medical director for infection prevention at Beaumont Health, which runs eight hospitals in the Detroit area and has more than 800 patients hospitalized.

The White House said on April 12 it was prepared to send additional therapeutic treatments to the state of Michigan but declined to promise more vaccines. (Reuters)

Michigan officials have pleaded with the White House for more vaccine doses, but the Biden administration has said it will stick to allocations based on state populations. Administration officials stressed that vaccines aren’t rapid-response tools for outbreaks.

“What we need to do in those situations is shut things down,” Rochelle Walensky, director of the Centers for Disease Control and Prevention, said Monday. “We need that vaccine in other places. If we vaccinate today, we will have, you know, impact in six weeks, and we don’t know where the next place is going to be that is going to surge.”

Along with Michigan, 32 other states have registered increases in infections in the past two weeks, including all the states along the Great Lakes, from Wisconsin to Pennsylvania. Minnesota and South Dakota are also up, making the Upper Midwest the major regional center of the spring wave. If there’s a single broad trend, it’s that the northern tier of the country is generally faring worse than the southern — for the moment.

Other regional hotspots include Maine and New Hampshire in northern New England; Delaware and Maryland in the Mid-Atlantic; Arizona, Colorado and Nevada in the Mountain West; and Oregon and Washington in the Pacific Northwest.

“In a nutshell, the increasing trend is concerning — covid-19 is clearly alive and well,” said Jeffrey S. Duchin, health officer for Seattle and King County. “It’s causing a large number of illnesses in young and middle-aged adults right now.”

By contrast, much of the Deep South, with the exception of Florida and Georgia in recent days, has reported sharp decreases. Since the winter wave ended, numbers in West Texas and the Great Plains have improved.

“The spring wave has not had a huge amplitude nationally, but has been very regional,” said David Rubin, director of PolicyLab at Children’s Hospital of Philadelphia.

He and his colleagues have pointed to weather and seasonality as factors in infection rates, with warmer and lengthening days supporting less virus transmission.

“There’s a clear latitude effect. If you go up into Canada, they’ve been having a really hard time,” he said.

The vaccination campaign appears to have altered the demographics of hospitalizations: With a large majority of elderly people now inoculated, the average age of patients has dropped. Gilpin, of Beaumont Health, said patients are generally less ill than in previous phases of the pandemic.

As of Thursday, more than 76 million people in the United States have been fully vaccinated. The vaccines are not foolproof, however — something known since the first results emerged from clinical trials. The CDC said Thursday that 5,800 cases of post-vaccination “breakthrough infections” have been reported nationwide. That’s fewer than 1 in every 13,000 vaccinations.

Of those breakthrough cases, 29 percent were asymptomatic and 7 percent required hospitalizations. CDC spokeswoman Kristen Nordlund said 74 of those vaccine recipients who had breakthrough infections died.

Separately, officials in Washington state reported Wednesday that 217 people among the 1.7 million fully vaccinated there have had breakthrough infections. Five deaths among patients ranging in age from 67 to 94, all with multiple underlying conditions, are under investigation, the state health department said.

Anthony S. Fauci, President Biden’s chief medical adviser on the pandemic, said during Monday’s White House task force news conference that there are two distinct types of vaccine failure.

“Primary vaccine failure” is when the body doesn’t mount a robust immune response. That could be caused by poor health, age, medication or something wrong with the vaccine. “Secondary vaccine failure” is when immunity fades over time, or if the person is exposed to a different virus strain.

“However, even if a vaccine fails to protect against infection, it often protects against serious disease,” Fauci said.

The CDC said these breakthrough infections were found in all age groups. Women accounted for 65 percent of reported breakthrough cases. The CDC did not break down the cases by vaccine type.

“To date, no unexpected patterns have been identified in case demographics or vaccine characteristics,” Nordlund said. She added that the CDC continues to advise vaccinated people to take precautions in public places, such as wearing masks, maintaining social distance, and avoiding crowds and poorly ventilated areas.

The nation appears to be moving forward, if not always smoothly, toward its goal of crushing the pandemic. By the end of the week, the United States is poised to reach the milestone of 200 million vaccine shots into arms, and the now-rapid pace of inoculations among the most vulnerable populations is driving down mortality rates from covid-19.

But vaccine hesitancy is much on the mind of public health officials. In coming weeks, the supply of doses may outstrip demand. Biden administration officials said Wednesday that the country is averaging 3.3 million vaccine doses a day.

Inoculations with the Johnson & Johnson vaccine were paused nationwide amid reports that six women between the ages of 18 and 48 suffered a rare blood clotting disorder. One of them died.

That number is small compared with the 7.5 million doses delivered, but the similarity of the cases to blood clotting seen in Europe in the rollout of the AstraZeneca vaccine — which uses a similar vector for introducing the vaccine into the body — has grabbed the attention of the scientific community.

This country’s vaccination efforts have relied far more heavily on the Pfizer-BioNTech and Moderna vaccines. But Johnson & Johnson has been ramping up in recent weeks, with 344,000 vaccinations reported Monday before the pause.

Any attempt to forecast the future of the pandemic has been hampered by unknowns about the virus and the human immune response to it, the unpredictability of human behavior, the successes or failures in persuading people to get vaccinated, and many other crosscurrents that can push infection and hospitalization numbers in opposite directions. Changing metaphors: Many dials are controlling this situation, manipulated simultaneously, clockwise and counterclockwise.

One dial involves the speed of vaccination. That took a setback this week with the Johnson & Johnson pause.

That is not a showstopper given that Johnson & Johnson has represented only about 5 percent of vaccinations. But the news was unwelcome in Michigan. The worries about this one vaccine could erode confidence in the broader vaccination campaign and the assurances of public health experts, at a moment when vaccines are the most powerful tool for ending the pandemic, Gilpin said.

“You’ve already got a pretty concerned chunk of the population that are already skeptical of the vaccine. This is not going to help,” he said. “This has become a race, a race to get the vaccine into people as quickly as possible before the virus can continue to spread, or continue to mutate. And so this will slow us down.”

Rubin, of Children’s Hospital, said human behavior is the biggest cause of recent infection upticks. Fatigued by the pandemic, people are lowering their guard, traveling more readily and socializing indoors with unvaccinated people. Governors and mayors are easing restrictions on gatherings.

“The biggest driving force of the spring resurgence has been how quickly the American people have abandoned social distancing,” Rubin said.

One of the big unknowns is the number of people who already have been infected with the virus and may have at least partial immunity. The official count is 31 million, but some experts think the true number is many times that. Some states hammered by high numbers of infections earlier in the pandemic, such as Iowa, have recorded more modest spring numbers, while states such as Maine and New Hampshire, largely spared until now, are seeing sharp spikes in cases.

On Tuesday, the country’s seven-day daily average for new infections topped 71,000 for the first time since Feb. 18.

Federal coronavirus data released Wednesday showed 1,414 counties color-coded as red, with “high transmission” rates, a rise from 1,317 on March 14. There was a mirror image to that increase: The number of counties color-coded blue, “low transmission,” also rose in the same time period, from 186 to 249.

Within states, the trends are not uniform. In Georgia, whose average of new cases increased more than 17 percent in the past week, 38 of its counties — many in the north and west of the state — have registered case average increases, while 52 have experienced decreases and the 67 other counties reported no change.

The northern states such as Michigan and Minnesota may have reached a peak in cases, as the upward trend of new infections has flattened in recent days. Rubin said modeling by Children’s Hospital of Philadelphia suggests that those states, as well as the New York City area, could soon experience declining infections. The forecasts are based in part on widespread drops in test positivity percentages that have consistently foreshadowed declines in caseloads and hospitalizations, Rubin said.

Highly contagious, mutation-laden variants of the virus are circulating. A variant first seen in the United Kingdom, known as B.1.1.7, and thought to be at least 50 percent more transmissible, is now the dominant strain in the United States, according to the CDC. Several other less-common variants are in the mix. The vaccines work against the variants for now, but evolution of the virus could necessitate changes in the vaccines similar to the reformulation of seasonal flu shots.

“There are these variants that are wild cards. But one thing we know for sure is if a virus can’t circulate, if it can’t replicate, it can’t create new variants,” said Ellen F. Foxman, an immunologist at Yale School of Medicine.

That points to the need for mass vaccination, she said, and the Johnson & Johnson vaccine pause shouldn’t derail the campaign.

“You want normal life? That’s your ticket, mass vaccination,” Foxman said. “We don’t want to let this one little bump of this very rare complication of this one vaccine to interrupt the progress that we’ve been making.”

Lena H. Sun contributed to this report.