C.D.C. to Recommend Some Vaccinated People Wear Masks Indoors Again

The Centers for Disease Control and Prevention recommended on Tuesday that people vaccinated against the coronavirus resume wearing masks in schools and in public indoor spaces in parts of the country where the virus is surging, marking a sharp turnabout from their advice just two months ago.

The pandemic in the United States is very different than it was in May, when it seemed as if the worst was in the past. Confirmed cases are surging in parts of the country with low vaccination rates, and there are more reports of breakthrough infections with the highly contagious Delta variant in fully immunized people.

Vaccines are effective against the worst outcomes of infection, even with the variant, and conditions are nowhere near as bad as they were last winter. But the new guidance amounts to a weary acknowledgment that the lagging vaccination effort has fallen behind the ever-evolving virus. Fewer than 50 percent of the country is fully vaccinated, according to federal data.

“This is not a decision we at C.D.C. have made lightly. This weighs heavily on me,” Dr. Rochelle P. Walensky, director of the C.D.C., said at a news briefing on Tuesday.

Here’s what we know:

The C.D.C. has long recommended that unvaccinated people wear masks indoors. But Tuesday’s regulations mean that even people who have been completely inoculated will once again need to mask up in public indoor spaces in parts of the country where the virus is ascendant.

In schools, health officials now recommended universal masking, regardless of vaccination status and community transmission of the virus, and additional precautions for staff, students and visitors. But they should still plan on returning to in-person learning in the fall.

How this will play out in states that have prohibited mask mandates in schools remains to be seen as well as communities where people may be weary of wearing masks.

The C.D.C.’s earlier recommendations were based on data that suggested that vaccinated people rarely become infected and almost never transmit the virus.

As recently as last week, a C.D.C. spokesman said that the agency had no plans to update its guidance. But the Delta variant, which now accounts for the bulk of infections in the United States, changed all that.

The Delta variant is thought to be about twice as contagious as the original version of the virus. Some research now suggests that people infected with the variant carry about a thousandfold more virus than those infected with other variants, and may stay infected for longer.

C.D.C. officials were persuaded in part by new scientific evidence showing that even vaccinated people may become infected and may carry the virus in great amounts, according to three federal officials with knowledge of the discussions. Even vaccinated people may carry great amounts of the variant virus in the nose and throat, hinting that they also may spread it to others, according to three federal officials familiar with the matter.

“The Delta variant is showing every day its willingness to outsmart us,” Dr. Walensky said at the news briefing. “In rare occasions, some vaccinated people infected with a Delta variant after vaccination may be contagious and spread the virus to others.”

Data from several states and other countries show that the variant behaves differently from previous versions of the coronavirus, she added: “This new science is worrisome and unfortunately warrants an update to our recommendation.”

In the past, Dr. Walensky has said the nation is in a “pandemic of the unvaccinated” — a point she reiterated on Tuesday. But she also said that she is concerned that vaccinated people who are in a place with substantial or high transmission could contract a breakthrough infection, and could pass the virus onto unvaccinated family members or those with weakened immune systems and others most at risk.

The C.D.C. is now conducting outbreak investigations in clusters, Dr. Walensky said. Officials are examining the amount of virus in breakthrough infections, which she said is “pretty similar” to the amount of virus in unvaccinated people. With the earlier Alpha variant officials did not believe a vaccinated person could transmit the virus, she said.

“The virus is changing, we are dealing with a dynamic situation,” said Dr. Anthony S. Fauci, the Biden administration’s top pandemic adviser. The C.D.C. is correct to revisit its recommendations as the virus evolves, he said.

“I don’t think you can say that this is just flip-flopping back and forth,” he added. “They’re dealing with new information that the science is providing.”

But that was before the arrival of the Delta variant, which now accounts for the bulk of infections in the United States. C.D.C. officials were persuaded by new scientific evidence showing that even vaccinated people may become infected and may carry the virus in great amounts, Dr. Walensky acknowledged at the news briefing.

But she said masking is only a “temporary measure,” and, adding, “What we really need to do to drive down these transmissions in the areas of high transmission is to get more and more people vaccinated and in the meantime, to use masks.”

The C.D.C. should have simply made a universal recommendation and told all Americans to wear masks indoors, said Ali Mokdad, an epidemiologist at University of Washington and former C.D.C. scientist. “The director said the guidance is for people in areas of high transmission, but if you look at the country, every state is seeing a rise in transmission,” Dr. Mokdad said. “So why not say, ‘Everybody in the U.S. should be wearing a mask indoors?’ The whole country is on fire.”

Daniel E. Slotnik contributed reporting.

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