Brian Pierce, the coroner in Baldwin County, Ala., thought he had seen the last of the coronavirus months ago as the area’s death count held steady at 318 for most of the spring and summer. But then in July and August, the fatalities began mounting and last week, things got so bad, the state rolled a trailer into his parking lot as a temporary morgue.“I think most people were thinking, ‘We’re good,’ ” he said. “Life was almost back to normal. Now, I’m telling my kids again to please stay home.”

Nationally, covid-19 deaths have climbed steadily in recent weeks, hitting a seven-day average of about 1,500 a day Thursday, after falling to the low 200s in early July — the latest handiwork of a contagious variant that has exploited the return to everyday activities by tens of millions of Americans, many of them unvaccinated. The dead include two Texas teachers at a junior high, who died last week within days of each other; a 13-year-old middle schoolboy from Georgia; and a nurse, 37, in Southern California who left behind five children, including a newborn.

What is different about this fourth pandemic wave in the United States is that the growing rates of vaccination and natural immunity have broken the relationship between infections and deaths in many areas.

The daily count of new infections is rising in almost every part of the country, according to data tracked by The Washington Post. But only some places — mostly Southern states with lower vaccination rates — are seeing a parallel surge in deaths. The seven-day average of daily deaths is about a third of what it was in January, the pandemic’s most deadly month, but it is forecast to continue rising as high numbers of patients are hospitalized.

While most regions with increasing deaths have lower vaccination rates, that isn’t the case for all of them.

Florida, for example, where more than 53 percent of the population is fully vaccinated, is the worst-hit state in terms of daily deaths, which have averaged 325 over the past week, alongside almost 20,000 new daily infections on average. Despite resistance from local school boards, Florida Gov. Ron DeSantis (R) has fought to enforce his ban on mask mandates and made good on a threat to withhold salaries from some of them this week even after a judge ruled the ban unconstitutional.

David Wesley Dowdy, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health, said the situation underscores the unanswered questions about the virus 18 months out — and the limitations of mathematical forecasting to predict the daily choices of 330 million Americans.

“The driving factor in the current wave is human behavior — how people interact and how people respond to risk — and that is really very unpredictable,” he said.

“We are in a perfect storm of viral changes and behavioral changes,” agreed Lauren Ancel Meyers, director of the University of Texas COVID-19 Modeling Consortium.

Virtually every time that humans have underestimated the virus and let down their guard, deaths surged.

Deborah Birx, then the coordinator of President Donald Trump’s coronavirus task force, suggested in March 2020, that mitigation measures might keep deaths at 100,000 to 240,000 under the most optimistic scenario. But by the end of 2020, when vaccines were first authorized for emergency use, the nation had long surpassed those numbers, and forecasters predicted U.S. covid-19 deaths would top out at around 550,000.

As of Thursday, the country has logged more than 640,000 deaths — and many experts believe we are not yet at the peak.

Difficult to predict

When looking at coronavirus deaths, the United States looks like two very different countries with a mostly north-south divide.