Chickenpox is one of the most contagious viruses known. An individual can spread the virus to as many as “90% of the people close to that person,” reports the CDC.

Is the delta variant that contagious as well?

The short answer is no, says evolutionary biologist and biostatistician Tom Wenseleers at the University of Leuven in Belgium, reports NPR.

“For the delta variant, the R0 is now calculated at between six and seven,” biologist and biostatistician Wenseleers notes. So it’s two- to three-times as contagious as the original version of SARS-CoV-2 (R0 = 2 to 3) but less contagious than the chickenpox (R0 = 9 to 10).

So why did the CDC say the delta variant was “just as transmissible as” the chickenpox?

For one, the leaked document underestimated the R0 for chickenpox and overestimated the R0 for the delta variant. “The R0 values for delta were preliminary and calculated from data taken from a rather small sample size,” a federal official told NPR. The value for the chickenpox (and other R0s in the slideshow) came from a graphic from The New York Times, which wasn’t completely accurate.

Yet Another Anonymous Source

“At the end of the day, this delta variant is much more transmissible than the alpha variant,” the official added. “That’s the message people need to take from this.”

The official requested anonymity because they were not authorized to speak to the media on this topic.