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. The data behind an internal US Centers for Disease Control and Prevention document that suggests fully vaccinated people might spread the Delta variant at the same rate as unvaccinated people is, according to the Washington Post, based on a Covid-19 cluster that emerged from July 4 weekend festivities in Provincetown, Massachusetts. Alex Morse, Provincetown’s town manager, told CNN’s “New Day” that there are 112 active cases right now in the town, but the overall cluster number is more than 880 since July 1.
Vaccination by itself is not enough to stop the spread of Covid-19 variants, study finds
Vaccination alone won’t stop the rise of new variants and in fact could push the evolution of strains that evade their protection, researchers warned Friday. They said people need to wear masks and take other steps to prevent spread until almost everyone in a population has been vaccinated. “When most people are vaccinated, the vaccine-resistant strain has an advantage over the original strain,” Simon Rella of the Institute of Science and Technology Austria, who worked on the study, told reporters. “This means the vaccine resistant strain spreads through the population faster at a time when most people are vaccinated.”
The findings suggest that policymakers should resist the temptation to lift restrictions to celebrate or reward vaccination efforts. This is likely to be especially true with a more transmissible variant such as the Delta variant, said Fyodor Kondrashov, also of the Institute of Science and Technology Austria. “Generally, the more people are infected, the more the chances for vaccine resistance to emerge. So the more Delta is infectious, the more reason for concern,” Kondrashov told reporters. “By having a situation where you vaccinate everybody, a vaccine resistant mutant actually gains a selective advantage.” People should not complain, he said. “The individual who already vaccinated and putting on a mask should not think this is pointless but should think that there is a vaccine resistant strain running around,” he said.