The agency stepped up concern over the spread of the virus in its report on Friday, urging even jurisdictions with undetectable levels of the virus to put into effect precautions. But the C.D.C.’s internal document sounded a significantly more alarmed note, advocating for universal masking — for everyone, whatever the local transmission levels — and recommending that the agency “acknowledge the war has changed.”
With the number of daily cases up to nearly 72,000 cases on average as of Friday, immunized people with young children, aging parents, or friends and family with weak immune systems may need to wear masks to protect vulnerable people in their orbit — even in communities with lower infection rates.
Indeed, the questions now facing Americans seem nearly inexhaustible, almost insoluble. Should companies really return employees to workplaces if vaccinated people might on occasion spread the variant? What does this mean for shops, restaurants, schools? Are unmasked family gatherings again off the table?
Delta’s unpredictable nature has humbled scientists who had anticipated that the virus would cause mostly sporadic outbreaks in areas with low rates of vaccination. In Britain, where the variant seems to be subsiding after a surge, vaccinations were rolled out by age, and a much higher proportion of people over 50 are vaccinated than in the United States.
But vaccination rates are much more patchy in the United States, said Bill Hanage, an epidemiologist at the Harvard T. H. Chan School of Public Health. “The upshot is that what Delta does in the U.K. is not necessarily what it’s going to do in places which have more very varied vaccination,” he said.
“Things are going to be worse than they would have been” without the variant, he added. “But they’re going to be much better than they might have been without vaccination.”
Understand the State of Vaccine Mandates in the U.S.
In the report published on Friday, the agency described a single outbreak in Provincetown, Mass., that quickly mushroomed to nearly 469 cases in the state as of Thursday, three-quarters of whom were fully immunized.