CDC Reports Vaccinated Persons Rarely Can Spread the Virus

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In another unexpected and unwelcome turn in the country’s pandemic, fully vaccinated people have so-called breakthrough infections. Delta variant The Centers for Disease Control and Prevention said in a report released Friday that the virus can spread to others as easily as unvaccinated people.

Vaccines remain strongly effective against severe illness and death, and infections are considered relatively rare in vaccinated persons. But the revelation follows a series of other findings this week about the Delta variant that have upended scientists’ understanding of the coronavirus.

In its report released Friday, the agency described a single outbreak in Provincetown, Mass., which quickly spread to about 469 cases in the state, three-quarters of which were fully vaccinated on Thursday.

An internal agency document obtained by The New York Times on Thursday night raised even more distressing questions about the virus and its course. Taken together, data collected by the CDC questions the country’s plans to return to offices and schools this fall, and raises tough questions about the masking, testing, and other measures Americans hope are behind them.

As soon as possible, the research reported the agency’s decision this week to advise even vaccinated Americans to continue wearing masks in closed public spaces in communities where the virus has risen.

The agency concluded that even those who are vaccinated carry high levels of the virus if infected, noting that they can transmit the virus as often as those without the vaccine. If so, they may be contributing to increases in new infections, although possibly to a much lesser degree than those who were not vaccinated.

Head of the University of California Department of Medicine, Dr. “We spent a lot of time, energy, and treasure in the last year trying to understand this damn virus, how it works and everything it does,” said Robert Wachter. San Francisco.

It was “just jarring,” he added, to learn how the delta variant differs from the original virus. “The brain doesn’t like to be shaken like this all the time.”

Epidemic studies have shown that Delta is far more contagious than the original virus or seasonal flu, and as contagious as chickenpox, according to an internal document circulating at the CDC.

Breakthrough infections were always expected among vaccinated people, but vaccinated Americans were not expected to become new sources of infection until the Delta variant arrived.

Vaccines, in whatever form, remain the only reliable shield against the virus. About 97 percent of people hospitalized with Covid-19 nationwide are unvaccinated, according to data from the CDC.

“Full vaccination is very protective, including against Delta,” said Angela Rasmussen, a research scientist at the Vaccine and Infectious Diseases Organization at the University of Saskatchewan in Canada.

“Masks are a wise precaution, but the bulk of the transmission is among the unvaccinated and it’s still those who are most at risk,” he added.

The collected research underscores the urgency of increasing the vaccination rate in the United States and reducing the number of people susceptible to serious diseases. This week, the vaccination rate in the European Union surpassed the United States for the first time.

The agency raised concerns over the spread of the virus in its report on Friday, urging even jurisdictions with undetected virus levels to take action. But the CDC’s internal document sounded like a much more apprehensive note advocating universal masking for all—regardless of local transmission levels—and recommending that the agency “acknowledge that war has changed.”

With daily cases reaching an average of around 72,000 cases on Friday, vaccinated people with young children, aging parents, or friends and family with compromised immune systems may need to wear masks to protect vulnerable people in their orbit, even in communities. with lower infection rates.

In fact, the questions facing Americans now seem almost inexhaustible, almost insoluble. Should companies really send workers back to work if vaccinated people can occasionally transmit the disease? What does this mean for shops, restaurants, schools? Are unmasked family gatherings off the table again?

The delta’s unpredictable nature humiliated scientists, who predicted that the virus would cause mostly sporadic outbreaks in areas with low vaccination rates. In Britain, where the variant seemed to decline after an increase, vaccines were distributed by age, and a much higher proportion of people over 50 were vaccinated at a much higher rate than in the United States.

But Bill Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health, said vaccination rates in the United States are much more erratic. “Ultimately, what Delta is doing in the UK is not what it would do where there is a much more diverse range of vaccines,” he said.

Without the variant, “things will be worse than they should be,” he added. “But they will be much better than they would have been without the vaccine.”

The outbreak in Provincetown, Massachusetts this month strongly supports the idea that even fully vaccinated people can spread the virus unknowingly. CDC director Dr. “We believe they may be on an individual level, so we’ve updated our recommendation,” Rochelle Walensky said in an email to The Times this week.

The epidemic sprouted after more than 60,000 revelers celebrated the 4th of July in Provincetown by gathering, often indoors, in busy bars, restaurants, guesthouses and rental homes.

By July 10, there was a noticeable increase in cases among residents of the district, including fully vaccinated people. A week later, the county’s daily average rose from zero to 177 cases per 100,000 people.

Dr. “Vaccines are like hippos,” Rasmussen said. “If you cross a river they will keep you dry, but if you go too deep the water starts to flow from the top. That seems to be what happened in the Massachusetts epidemic.”

Three-quarters of people infected in Provincetown reported coughing, headache, sore throat or fever (signs of infection in the upper respiratory tract), and 74 percent were known to be fully vaccinated.

Four out of five hospitalized people were fully vaccinated, one with the Pfizer-BioNTech vaccine and three with the Johnson & Johnson vaccine. Two of the patients had underlying medical conditions. Genetic analysis of 133 cases identified the Delta variant in 119 and a closely related virus in one case.

scientists warned even last year that vaccines may not completely prevent infection or transmission. But experts did not expect these events to play a significant role in combating the virus, nor did they predict how quickly the Delta variant would rip the country apart.

Dr. “I thought we drove over the mound two months ago,” Wachter said. In San Francisco, the nation’s largest city with the highest vaccination rates, 77 percent of people over the age of 12 are vaccinated.

Yet the hospital where he works has seen a sharp rise from one Covid-19 case on June 1 to 40. 15 of the patients are in intensive care.

Dr. “If reaching 70 or 75 percent immunity doesn’t protect the population, I think it’s very difficult to predict what happens to a place that’s 30 percent vaccinated,” Wachter said. “Humility may be the most important thing here.”

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