C.D.C. Internal Report Calls Delta Variant as Contagious as Chickenpox
The Delta variant is much more contagious, more likely to break the protections offered by vaccines, and can cause more serious illness than any other known version of the virus, according to an internal presentation released to the Centers for Disease Control and Prevention.
Agency director Dr Rochelle P. Walensky admitted on Tuesday that people vaccinated with so-called “breakthrough” infections of the Delta variant carried as much virus in their nose and throat as unvaccinated people. But the internal document presents a broader and darker view of the variant.
The Delta variant is more transmissible as the viruses that cause MERS, SARS, Ebola, colds, seasonal flu and smallpox, and it’s as contagious as chickenpox, according to the document, a copy of which was obtained by The New York Times.
The immediate next step for the agency is to “recognize that the war has changed,” the document says. Its contents were first reported by the Washington Post on Thursday evening.
The tone of the document reflects the concern of scientists at the CDC about the spread of Delta across the country, said a federal official who saw the research described in the document. The agency is expected to release additional data on the variant on Friday.
“The CDC is very concerned about the data coming in that Delta is a very serious threat that requires action now,” the official said.
There were 71,000 new cases per day on average in the United States as of Thursday. The new data suggests that people who have been vaccinated are spreading the virus and contributing to these numbers – although likely to a much lesser degree than those who are unvaccinated.
Dr Walensky called transmission from vaccinated people a rare event, but other scientists have suggested it may be more common than previously thought.
The agency’s new masking guidelines for those vaccinated, presented on Tuesday, were based on information presented in the document. The CDC has recommended that vaccinated people wear masks indoors in public places in communities with high transmission of the virus.
But the internal document suggests that even that recommendation might not go far enough. “Given the higher transmissibility and current vaccine coverage, universal masking is essential,” the document said.
Agency data suggests that people with weakened immune systems should wear masks even in places where virus transmission is not high. The same goes for vaccinated Americans who come into contact with young children, older adults, or otherwise vulnerable people.
There are about 35,000 symptomatic infections per week among 162 million Americans vaccinated, according to data collected by the CDC as of July 24 that was cited in the internal submission. But the agency doesn’t track all mild or asymptomatic infections, so the actual incidence may be higher.
Infection with the Delta variant produces amounts of virus in the respiratory tract that are ten times greater than those seen in people infected with the Alpha variant, which is also highly contagious, the document notes.
The amount of virus in a person infected with Delta is a thousand times greater than that seen in people infected with the original version of the virus, according to a recent study.
The CDC’s paper draws on data from several studies, including an analysis of a recent outbreak in Provincetown, Massachusetts, which began after the city’s July 4 festivities. By Thursday, that group had grown to 882 cases. About 74% have been vaccinated, local health officials said.
Detailed analysis of the spread of cases has shown that people infected with Delta carry huge amounts of the virus in their noses and throats, regardless of their vaccination status, according to the CDC document.
“This is one of the most impressive examples of citizen science that I have seen,” said Dr. Celine Gounder, infectious disease specialist at Bellevue Hospital Center in New York City. “Those involved in the Provincetown outbreak have been meticulous in compiling lists of their contacts and exposures. “
Infection with the Delta variant may be more likely to lead to serious illness, the document notes. Studies in Canada and Scotland have found that people infected with the variant are more likely to be hospitalized, while research in Singapore has indicated that they are more likely to need oxygen.
Still, CDC figures show that vaccines are very effective in preventing serious illness, hospitalizations and death in those vaccinated, experts said.
“Overall, Delta is the troubling variant that we already knew it was,” said John Moore, virologist at Weill Cornell Medicine in New York City. “But the sky is not falling and vaccination still strongly protects against the worst outcomes.”
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