As for the virus itself, the country has been averaging fewer than 15,000 new coronavirus cases a day for nearly a month, the lowest levels since testing became widely available and a fraction of what was reported in January, when the nation routinely identified more than 200,000 cases in a day.
In recent days, however, the average number of new cases has started to trend slightly upward nationally, driven largely by localized outbreaks in places with low vaccination rates, including parts of Missouri, Arkansas and Nevada.
As the Delta variant has spreads across the globe, the World Health Organization recently reiterated its longstanding guidance that everyone, vaccinated or not, should wear masks as a precaution. In the United States, however, the C.D.C. has not changed its advice that those who are fully vaccinated can skip masks in most situations.
U.S. health officials have suggested that the W.H.O.’s blanket suggestion was informed by its global purview, since many countries have had far less access to vaccines than the United States.
In New York City, efforts to monitor the spread of the virus have been scaled back, reflecting a steadily low caseload and a sense held by many that the virus is less of a wide threat. More than 51 percent of residents are fully vaccinated, according to city data, though large parts of the city still have lower rates. Coupled with concerns about Delta, some public health experts and elected officials are worried that the city may be pulling back on its surveillance measures too soon.
On Tuesday, Jen Psaki, the White House press secretary, said that the Biden administration was unlikely to impose new national mitigation measures, even if cases rise.
“The states are going to have to make evaluations and local communities are going to have to make evaluations about what’s in their interests,” she said.
Mitch Smith and Sharon Otterman contributed reporting.