An earlier version of this story misstated the role Ken Langone had with Home Depot. He is a co-founder of the now publicly traded company but has no management control.

New federal mask guidance left Americans scrambling Wednesday to determine whether to increase their coronavirus precautions as the uber-transmissible delta variant threatened the nation’s progress against the pandemic. The announcement served as a dismal acknowledgment that infections in the United States have quadrupled in July, even as highly effective vaccines are widely available.

Here are some significant developments:

  • The Centers for Disease Control and Prevention on Tuesday said vaccinated people in high-transmission areas may be able to spread the coronavirus and should resume wearing face coverings.
  • The CDC also newly suggested that everyone older than 2, vaccinated or not, should wear face coverings in school buildings.
  • Some states and cities, including Nevada and Kansas City, Mo., quickly reinstated mask mandates after federal officials released their new guidance. Others, including California, Oregon and Washington, issued “recommendations” that vaccinated people wear masks.
  • Coronavirus cases are increasing almost exclusively among unvaccinated people, a Washington Post analysis found. Those people are most affected in areas where the delta variant is most common.
  • Corporate chief executives expressed concern about bringing employees back to crowded offices in the coming months as Google said it would push back its return from September to October.
  • The resident physician on Capitol Hill ordered the House of Representatives to resume wearing face coverings to prevent spread among members and staff.

CDC Director Rochelle Walensky on Wednesday defended her agency’s mask guidance from criticism that the evolving rules are confusing.

Top health officials Anthony S. Fauci and Rochelle Walensky said July 28 that vaccinated individuals should wear masks indoors, per new CDC guidance. (The Washington Post)

In an interview on “CBS This Morning,” she said guidance given in May that fully vaccinated people could go sans mask was based on evidence that the delta variant made up only 1 percent of the virus in circulation.

Most infections in the U.S. are now delta, which Walensky called “a different kind of beast.” She said new data shows that vaccinated people who get a rare breakthrough infection can pass the virus to others.

Walensky emphasized that the nation can change course by shifting behavior.

“We can do something if we unify together, if we get people vaccinated who are not yet vaccinated, if we mask in the interim,” she said. “We can halt this in just a matter of a couple of weeks.”

Anthony S. Fauci, the federal government’s top infectious-disease expert, said the mask guidance is primarily meant to protect vulnerable people whom vaccinated people with breakthrough infections might encounter. He also backed the CDC’s decision.

“Something has changed, and what has changed is the virus,” Fauci said on MSNBC. “The CDC hasn’t changed, and the CDC hasn’t really flip-flopped at all.”

Fauci added that increasing vaccinations would help prevent the coronavirus from mutating further in ways that could better evade the vaccines.

Others questioned how much the CDC’s guidance would affect case numbers. Former Food and Drug Administration director Scott Gottlieb said he doubted the revised advice would change the landscape because little transmission is occurring among vaccinated people.

“I think that’s going to be very little bang for our buck in terms of trying to reduce transmission right now in the context of this wave of infection,” he told NPR’s “Morning Edition.”

Gottlieb added that the country’s reported average of nearly 62,000 daily infections is probably an undercount. That means the U.S. is probably closer to the end than the beginning of the delta wave, he said.

Public officials continue to push vaccinations in the face of lethargic immunization rates. Starting Friday, anyone who gets their first dose at a site run by New York City will automatically receive $100. Senate Minority Leader Mitch McConnell (R), meanwhile, said he planned to use money from his reelection campaign to fund pro-vaccination ads on more than 100 Kentucky radio stations.

Increasing numbers of employers have also signaled a willingness to compel vaccinations. As President Biden planned to announce that federal workers must get immunized or submit to regular testing, the state of New York joined California and New York City in announcing a similar requirement for employees.

In the private sector, billionaire investment banker Ken Langone, a co-founder of Home Depot, told CNBC’s “Squawk Box” that he planned to require vaccinations at his companies after the FDA gives the shots full approval. The Washington Post announced Tuesday that it would require all employees to be vaccinated by mid-September, with exceptions for medical and religious reasons. And Google said it would require immunization and push back its date for returning to the office from September to October due to the delta variant.

Restaurants are also increasingly requiring the shots as a condition to dining. Armando Celentano, owner of the gastropub Argosy in Atlanta, told CNN he was trying to create a safer working environment for his employees. But he acknowledged he does not have enough staff members to actually check patrons’ vaccination cards at the door.