After a steady decline since mid-September, coronavirus cases are once again rising in most of the United States. New cases have increased by 25 percent nationally in the past two weeks. In 14 states, cases have climbed by 40 percent or more.
Some of the biggest spikes have been in the Midwest, a region where Covid-19 cases hit an all-time high around this time last year. Michigan and Minnesota, which had only modest waves during the late-summer surge, are now seeing the most cases per capita in the country.
Daily average new cases in the Midwest
Nationally, the daily average number of hospitalized Covid patients is about 50,000, half what it was during the September peak. But in most states where cases have risen drastically in the past two weeks, hospitalizations are also starting to rise.
Hospitalizations in states where new cases are surging
Note: States where cases have risen at least 40 percent in the past 14 days are shown.
The overall vaccination rate is higher in the United States now than it was during the summertime wave, meaning more people are protected from severe disease. But waning immunity could also play a role, said Lauren Ancel Meyers, an epidemiologist at The University of Texas.
“We may have higher levels of immunity in many U.S. communities, acquired through a combination of primary vaccines, booster doses and recent infections,” Dr. Meyers said. “However, waning immunity means that people who were infected early in the pandemic or received their last dose of vaccine more than six months ago may once again be vulnerable to severe infections.”
And, Dr. Meyers added, “the important wild card is behavior. Risks can increase because of relaxation in Covid-19 policies, pandemic fatigue, and organic shifts in how we move and gather with the onset of winter weather and the holiday season.”
Last year, Thanksgiving travel appeared to contribute to isolated outbreaks around the country.
In the Northeast, where vaccination rates are high, most states had only modest surges in the late summer, but in many of them, cases have been trending upward since early November.
Daily average cases in the Northeast
Note: New Hampshire cases from Oct. 26 to Oct. 31 are not shown because of a data anomaly.
In New Jersey, where cases are up 66 percent in the past two weeks, rates of severe disease have so far remained moderate. In a news conference on Monday, Judith Persichilli, the New Jersey Department of Health commissioner, noted that the state’s current hospitalization rate — around 830 — was far lower than its peak in January. In that month, Times data shows, Covid hospitalizations in the state neared 4,000.
“I think the bigger difference this year is that we have many more people vaccinated,” Ms. Persichilli said. She warned, however, that the state could still reach a hospitalization rate of 2,000 or more.
In the West, case rates in coastal states — California, Oregon and Washington — have stayed relatively low, while the Four Corners states — Arizona, Colorado, New Mexico and Utah — have seen high rates of transmission in recent weeks. In the northern part of the region, cases in Idaho, Montana and Wyoming have abated somewhat from worrisome recent peaks but remain high.
Daily average new cases in the West
Southern states, where vaccination rates have remained relatively low, got the worst of the late-summer surge, and intensive care units in much of the region were overflowing just 10 weeks ago. Cases in the region had been declining since that peak, but in some states are again beginning to tick upward.