One influential model, produced by the Institute for Health Metrics and Evaluation at the University of Washington, predicts a modest overall surge in cases, hospitalizations and deaths this fall. Scott Gottlieb, a former head of the Food and Drug Administration, said Sunday that a fall surge could occur even if 75 percent of the eligible population is vaccinated.
But experts think that most damage will occur in localized pockets where large numbers of people have declined to be vaccinated or have not gained access to the shots.
“I think a rise in cases is certainly going to happen,” said William Hanage, an associate professor of epidemiology at the Harvard T.H. Chan School of Public Health. The question “is how large a rise and how consequential it’s going to be.”
“Those under-vaccinated communities are more likely to be severely” affected, he said.
At a briefing by the White House Covid-19 Response Team on Tuesday, Anthony S. Fauci, the nation’s top infectious-disease specialist, said “there is a danger — a real danger — that if there is a persistence of a recalcitrance to getting vaccinated, that you could see localized surges, which is the reason why I want to emphasize what all four of us have said: All of that is totally and completely avoidable by getting vaccinated.”
Resistance is greatest among younger people. Just 38.3 percent of those ages 18 to 29 have been vaccinated, according to federal research released Monday. Across all age groups, people living in counties with high rates of poor and uninsured people and less access to computers and the Internet were less likely to be vaccinated, the research showed.
In general, rural and Republican areas have embraced vaccination less than cities and Democratic states in the Northeast and along the West Coast. All of the states in New England have given at least one dose to 61 percent of their residents or more. In San Francisco, 65 percent of residents are fully vaccinated.
Overall, the nation has made significant progress against the virus. The seven-day average of new daily cases has plummeted to 10,350, and deaths are down to an average of 273 each day, Rochelle Walensky, director of the Centers for Disease Control and Prevention, reported Tuesday. Those figures are a small fraction of average daily peaks of nearly 250,000 cases and 3,300 deaths in January.
In addition, with 80 percent of adults older than 65 vaccinated, the most vulnerable population is largely protected. That should mean many fewer deaths and hospitalizations even if another widespread surge were to occur this fall or winter.
But the delta variant, which is much more transmissible and causes more severe illness than previous versions of the virus, is taking over in the United States with stunning speed, as it did in India, where it was first identified, and later in the United Kingdom. It has doubled as a percentage of new infections every two weeks, Fauci said, from 1.2 percent of new infections on May 8 to 20.6 percent this week. Officials expect it to soon become the dominant strain in the United States.
Helix, a lab company working with the CDC to sequence samples, also concluded that the delta variant and the gamma variant, first identified in Brazil, are rapidly replacing the alpha variant, which was first identified in the United Kingdom and took over in a matter of months, according to research the company posted this week. The work has not yet been reviewed by experts not involved in the study.
The delta variant may accomplish the same thing within weeks.
“It has come out of nowhere,” said Mark Pandori, who runs the genomics lab at the University of Nevada at Reno. “It seems to be a very successful variant and is closing in on the number one spot.”
Pandori emphasized that the number of positive cases is low because they are in many parts of the country, and that the small number of breakthrough infections among those who have been vaccinated appears to confirm the immunizations’ effectiveness against current variants, including delta.
Pavitra Roychoudhury, a virologist at the University of Washington, said cases in the state have been almost exclusively caused by the alpha variant for several months. But in the past two weeks, cases of the delta and gamma variants have been increasing.
Karthik Gangavarapu, a researcher at the Scripps Research Institute in San Diego who works on genomic epidemiology, predicted that the delta variant may be responsible for more than 50 percent of cases by July, based on the volume that state labs are seeing. He said the numbers appear to confirm early studies that the variant may be 40 to 60 percent more transmissible than the alpha variant, which is already more transmissible than the original virus that emerged from Wuhan, China.
“I think the delta variant is troubling. I’m not going to lie,” he said.
In Britain, the delta variant, now responsible for more than 90 percent of new infections, last week forced the government to delay full relaxation of virus restrictions — dubbed “freedom day” by the tabloids — for four weeks.
About 64 percent of the population in the United Kingdom have received at least one shot, but only 46 percent are fully vaccinated.
Until now, Britain has focused on getting first shots to as many people as possible. In December, officials decided to delay the second jab, a policy U.S. health authorities resisted.
Public health officials pushed back the recommended vaccination schedules for the two approved vaccines at the time — three weeks for Pfizer-BioNTech and four weeks for AstraZeneca — to 12 weeks to distribute first shots to the largest possible number of people.
But concerns about the delta variant have upended that policy. The British government announced last week that people older than 40 in England and Scotland can now get their second jab at eight weeks instead of 12.
Stephen Griffin, an associate medical professor at the University of Leeds, said introducing the 12-week gap “was a gamble, but it was the right gamble at the time, given the variants that we had, because a single dose was effective against alpha.” But he said it “looks as if a single jab isn’t as protective as this new [delta] variant compared with alpha.”
“If you have a three-month gap between first and second jabs, that opens the playing field to having susceptible individuals out there for the virus to spread through.”
At a briefing two weeks ago, Fauci presented data from Britain’s public health agency showing that two doses of the vaccines made by Pfizer-BioNTech and AstraZeneca are 88 percent effective at preventing symptomatic disease caused by the delta variant. He said the Pfizer data would be similar to that of Moderna’s product, also an mRNA vaccine.
But one vaccine dose offers just 33 percent protection, the data shows, a reminder of how strongly the second shot boosts immunity to the virus.
The United States has endured regional outbreaks earlier in the pandemic. The virus first crashed through New York and the northeast in March and April of 2020, then tore through the Sun Belt last summer. In January, the entire country was engulfed by the highest caseloads and death counts of the pandemic.
But vaccines were not available then. Now they are. A Post analysis showed that as recently as the beginning of June, diverging vaccination rates did not predict a difference in caseloads. But about the middle of the month, the number of infections began to decrease markedly in places where many people were immunized and increase in areas where they are not.
The vaccines “are nearly 100 percent effective against severe disease and death, meaning nearly every death due to covid-19 is particularly tragic because nearly every death, especially among adults, due to covid-19 is, at this point, entirely preventable,” Walensky said Tuesday.
Now, experts say the trend will continue and grow more pronounced unless vaccination rates pick up in places where they are lagging. And the more the virus circulates, in the United States and the rest of the world, the greater the chances are that an even more transmissible or dangerous variant will emerge.
“There is light at the end of the tunnel, but it’s quite a dark tunnel,” Gangavarapu said. “As long as vaccination continues, we should be able to avert a further surge. But how this thing will pan out is still a question.”