In an alarming sign of the pandemic’s resurgence, the Centers for Disease Control and Prevention reversed course Tuesday and recommended that fully vaccinated people wear masks indoors in areas of higher transmission, including Boston, Cape Cod and the Islands, and Bristol County.
Citing new information about the Delta variant’s ability to spread among vaccinated people, federal health officials also recommended indoor masks for all students and staff at schools nationwide, regardless of vaccination status.
“We have new science related to the Delta variant that requires us to update the guidance,” for vaccinated people, CDC director Dr. Rochelle Walensky said. “Recent outbreak investigations show that the Delta variant behaves uniquely differently. In areas with substantial and high transmission, CDC recommends fully vaccinated people wear masks.”
In Massachusetts, where a sense of normalcy had been returning since late spring, the renewed warnings were a jarring reminder that the coronavirus remains resilient, despite high vaccination rates. The new CDC advisory currently applies to five counties in Massachusetts — Barnstable, Suffolk, Bristol, Nantucket, and Dukes — where transmission rates are considered high or substantial. About 60 percent of all US counties meet that standard.
The Baker administration, which lifted the state’s mask mandate in May, and state education officials said they were reviewing the new federal guidance, but declined to comment further. Boston public schools had previously mandated masks for students and staff this fall, but many districts remain undecided.
“Now is not the time to let our guard down, especially with the Delta variant, the most contagious we have seen,” said Merrie Najimy, president of the Massachusetts Teachers Association.
President Biden said Tuesday that he is considering a requirement that all federal workers be vaccinated, a day after the US Department of Veterans Affairs became the first federal agency to require vaccinations. Its 115,000 health-care workers face being fired if they refuse.
Biden dismissed concerns that the new masking guidance could invite confusion, saying the substantial number of people who have yet to get vaccinated are the ones “sowing enormous confusion.”
“The more we learn about this virus and the Delta variation, the more we have to be worried and concerned. And there’s only one thing we know for sure: If those other 100 million people got vaccinated, we’d be in a very different world,” he said.
On Monday, the state of California and New York City announced that hundreds of thousands of government workers will be required to be vaccinated or submit to weekly testing.
A spokesman for Baker declined to comment when asked if the governor was considering a vaccine requirement among state employees. And, in Boston, several rivals in the mayoral campaign put pressure on Acting Mayor Kim Janey to issue a similar directive for the city’s 18,000-person workforce.
But a Janey spokeswoman, Emma Pettit, said “there is no current mandate for COVID-19 vaccination,” but noted that masks are required inside all municipal buildings. City officials, she added, “will continue to use data to drive our decision-making and will adjust employee and public health guidance as necessary.” She said that any vaccine mandate would have to be collectively bargained with municipal employee unions.
As of July 20, Boston was averaging 46.6 new positive COVID cases each day. More than 60 percent of Boston’s total population has been fully vaccinated.
Dr. Shira Doron, an epidemiologist at Tufts Medical Center, said “drastic and aggressive” measures, such as vaccination mandates, are necessary to curb the spread of the Delta variant.
“The only way that we’re going to get out of this, the only way we’re going to be able to move forward instead of continually moving backwards, is to do something drastic about vaccinations,” Doron said. “The only way to do it is to mandate it where it can be mandated. The place to start is in public workers.”
On Tuesday, Massachusetts reported 657 new confirmed cases of coronavirus, 12 new confirmed deaths, and 7,098 additional vaccinations. More than 60 percent of its approximately 7 million residents have been fully vaccinated.
COVID deaths in the United States surged 48 percent over the past week to a daily average of 239, and hospitalizations also are rising. The Delta variant now makes up 83 percent of all COVID-19 cases, up from 50 percent at the beginning of July, according to the CDC.
More than 97 percent of hospitalized COVID patients are unvaccinated, but new evidence shows that fully vaccinated people can become infected and carry the virus, leading to more spread, Walensky said.
Vaccinated people “have the potential to spread that virus to others,” she said.
Local officials said the new federal guidelines underscored the danger the pandemic still poses. In Revere, Mayor Brian Arrigo said the city’s health department has been monitoring the rise in cases and is considering ways to combat the spread, which could include “potential vaccine requirements for city staff, updated mask mandates, and a strong look at policies and procedures for school reopening.”
“The City of Revere will continue to follow the science and take appropriate action,” he said.
In Chelsea, which is also in Suffolk County, City Manager Thomas Ambrosino said the city will share the new CDC guidance with the public, but is not considering mandating masks indoors for the time being.
Barnstable County is the only Massachusetts county rated at high risk, a designation that means 100 or more COVID cases per 100,000 people have been recorded over the past seven days. The other four counties are listed at substantial risk, which means that 50 to 99 cases per 100,000 people have been counted over the previous week.
The surge on Cape Cod has come at the height of tourist season. During an emergency meeting Sunday in Provincetown, local officials approved a new indoor mask mandate and a measure clearing the way for stricter capacity limits on local businesses amid a surge of COVID cases since the July Fourth weekend.
“COVID, unfortunately — and I think it’s depressing for many of us — isn’t going away anytime soon,” Town Manager Alex Morse said during the meeting. “Provincetown is experiencing what other places will be experiencing, earlier.”
The surge also is being felt in other parts of New England. The number of daily coronavirus infections has quadrupled in Maine over the last four weeks, and the total count there has eclipsed 70,000 cases since the start of the pandemic.
The seven-day rolling average of daily new cases has risen from about 14 new cases a day on July 11 to about 61.
Rhode Island is considered to have “substantial transmission” of the coronavirus, according to the CDC. Over the past week, there have been more than 57 new cases of COVID per 100,000 people.
The CDC’s new guidance followed recent decisions in Los Angeles and St. Louis to revert to indoor mask mandates amid a spike in COVID-19 cases and hospitalizations that have been particularly bad in the South. The country is averaging more than 57,000 cases a day and 24,000 COVID hospitalizations.
Across the United States, about 163 million people — about 49 percent of the population — are vaccinated, according to the CDC.
A map of COVID transmission in the United States shows large swaths of the country classified as “high transmission” areas. In states such as Missouri, Arkansas, Mississippi, and Alabama, almost every county is classified as “high.”
Danny McDonald and Amanda Kaufman of the Globe staff and Globe correspondents Nick Stoico and Kate Lusignan contributed to this report.