Delta variant spreads as easily as chickenpox: CDC

The Delta coronavirus variant surging across the world appears to cause more severe illness and spread as easily as chickenpox, according to an internal document from the US Centers for Disease Control and Prevention.

The document outlines unpublished data that shows fully vaccinated people might spread the Delta variant at the same rate as unvaccinated people, reports CNN.

CDC Director Dr Rochelle Walensky confirmed the authenticity of the document, which was first reported by The Washington Post.

"I think people need to understand that we're not crying wolf here. This is serious," she told CNN.

"It's one of the most transmissible viruses we know about. Measles, chickenpox, this -- they're all up there."

The CDC is scheduled to publish data Friday.

She said the data in the report did not surprise her. "It was the synthesis of the data all in one place that was sobering," she said.

The CDC presentation 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.

That infectivity is known as R0.

"When you think about diseases that have an R0 of eight or nine -- there aren't that many," Walensky told CNN.

And if vaccinated people get infected anyway, they have as much virus in their bodies as unvaccinated people. That means they're as likely to infect someone else as unvaccinated people who get infected.

"The bottom line was that, in contrast to the other variants, vaccinated people, even if they didn't get sick, got infected and shed virus at similar levels as unvaccinated people who got infected," Dr Walter Orenstein, who heads the Emory Vaccine Center and who viewed the documents, told CNN.

But vaccinated people are safer, the document indicates.

"Vaccines prevent more than 90 per cent of severe disease, but maybe less effective at preventing infection or transmission," it reads. "Therefore, more breakthrough and more community spread despite vaccination."

It says vaccines reduce the risk of severe disease or death 10-fold and reduce the risk of infection three-fold.

The presentation also cites three reports that indicate the Delta variant -- originally known as B.1.617.2 -- might cause more severe disease.

The CDC, the document advises, should "acknowledge the war has changed." It recommends vaccine mandates and universal mask requirements.

Earlier Thursday, US President Joe Biden announced a number of new steps his administration will take to try to get more Americans vaccinated, including requiring that all federal employees must attest to being vaccinated against Covid-19 or face strict protocols.