The Delta variant is much more contagious, is more likely to break vaccine protection, and can cause more serious illness than any other known version of the virus, according to an internal presentation circulating within the Centers for Disease Control and Control.
Agency director Dr Rochelle Walensky admitted on Tuesday that people vaccinated with so-called progressive Delta variant infections carry just as much virus in their nose and throat as unvaccinated people and can spread it just as easily, albeit less often.
The internal document, however, offers a broader and darker view of the variant. The Delta variant is more transmissible than the viruses that cause MERS, SARS, Ebola, the common cold, seasonal flu, and smallpox, and as contagious as chickenpox, according to the document copied by the New York Times. The immediate next step for the agency is "to realize that the war has changed," the document reads. The content was first reported by the Washington Post on Thursday evening.
The tone of the document echoes CDC scientists' concern about the spread of Delta across the country, said a federal official who saw the research outlined in the document. The agency is expected to publish further data on the variant on Friday. "The CDC is very concerned about the data they are entering that Delta is a very serious threat that now requires action," the official said. The US had an average of 71,000 new cases per day as of Thursday.
The new data suggest that vaccinated individuals spread the virus and contribute to these numbers, albeit likely to a much lesser extent than unvaccinated individuals. Walensky has called transmission from vaccinated people a rare occurrence, but other scientists have suggested that it is more common than previously thought. The agency's new masking guidelines for vaccinated individuals, released Tuesday, were based on information contained in the document, with the CDC recommending that vaccinated individuals wear masks in public facilities in communities with high levels of virus transmission indoors. However, the internal document indicates that even this recommendation may not go far enough.
"Given the increased transferability and current vaccination protection, universal masking is essential," the document says. Agency data suggests that people with weak immune systems should wear masks even in places with low virus transmission, much like vaccinated Americans who are in contact with young children, older adults, or vulnerable people.
There are approximately 35,000 symptomatic infections per week in 162 million vaccinated Americans, based on data compiled by the CDC July 24 and cited in the internal record, but the agency does not track all mild or asymptomatic infections, so the Incidence can be higher.