An internal report presented to the US Centers for Disease Control and Prevention indicates the Delta coronavirus variant is far more transmissible than older lineages, may cause more severe disease, and that when it causes breakthrough infections, may be as easily transmitted as when it infects unvaccinated people.
What the document shows:
- The slideshow dated Thursday and first obtained by The Washington Post, appears to provide some data backing CDC Director Dr. Rochelle Walensky’s controversial decision on Tuesday to change the agency’s guidance on mask use.
- It says the Delta variant is about as transmissible as chickenpox, with each infected person, on average, infecting eight or nine others. The original lineage was about as transmissible as the common cold, with each infected person passing the virus to about two other people on average.
- And if vaccinated people get infected anyway, they have as much virus in their bodies as unvaccinated people. But vaccinated people are safer, the document indicates. It says vaccines reduce the risk of severe disease or death 10-fold and reduce the risk of infection three-fold.
- The CDC, the document advises, should “acknowledge the war has changed.” It recommends vaccine mandates and universal mask requirements.
How the CDC reacted:
- Walensky confirmed to CNN that the slideshow was presented to her at a noon briefing on Thursday. “I think people need to understand that we’re not crying wolf here. This is serious,” Walensky told CNN Thursday night. “It’s one of the most transmissible viruses we know about. Measles, chicken pox, this – they’re all up there," she said.
- Walensky noted that the R0 for the Delta variant – a measure of its transmissibility – is estimated to be 5-9, meaning each infected person can be expected to infect 5-9 other people. “When you think about diseases that have an R0 of 8 or 9 – there aren’t that many.”
- Asked about the contents of the slide deck, Walensky said, “There weren’t any surprises. It was the synthesis of the data all in one place that was sobering.”
What comes next:
- The CDC is scheduled to publish additional data Friday that will back Walensky's controversial decision to change guidance for fully vaccinated people. She said Tuesday the CDC was recommending that even fully vaccinated people wear masks indoors in places where transmission of the virus is sustained or high.
CNN's Paul LeBlanc and Maggie Fox contributed reporting to this post.