Skip to main content

Sign up for our newsletter.

Quality journalism. Progressive values. Direct to your inbox.

People shop at a store enforcing mask-wearing requirements

People shop at a grocery store enforcing mask-wearing requirements in Los Angeles on July 23, 2021. (Photo: Chris Delmas/AFP via Getty Images)

'A Very Serious Threat': CDC Document Warns Delta Variant Is as Contagious as Chickenpox

"People need to understand that we're not crying wolf here," said the CDC director. "It's one of the most transmissible viruses we know about."

Jake Johnson

An internal slide presentation assembled by officials at the Centers for Disease Control and Prevention warns that the Delta variant of the coronavirus—now the dominant strain in the U.S. and across much of the world—is as transmissible as chickenpox, could lead to more extreme illness than earlier mutations, and can likely be spread by people who are fully vaccinated.

First obtained by the Washington Post on Thursday, the document (pdf) states that the "Delta variant may cause more severe disease than
Alpha or ancestral strains," citing data on hospitalizations and deaths in Canada, Scotland, and Singapore. While noting that people who are fully inoculated against Covid-19 can still catch and spread the Delta variant, the document stresses that vaccines are extremely effective in preventing severe illness and death.

"Delta is different from previous strains," one of the slides reads, summarizing that the variant is "highly contagious," "likely more severe," and "breakthrough infections may be as transmissible as unvaccinated cases." The presentation says Delta is more contagious than Ebola, the seasonal flu, the flu of 1918, and smallpox.

Dr. Rochelle Walensky, the director of the CDC, confirmed the authenticity of the leaked document in an interview with CNN.

"I think people need to understand that we're not crying wolf here. This is serious," Walensky said. "It's one of the most transmissible viruses we know about. Measles, chickenpox, this—they're all up there."

An unnamed federal official told the New York Times that the CDC is expected to publish additional data on the Delta variant on Friday.

"The CDC is very concerned with the data coming in that Delta is a very serious threat that requires action now," the official said.

Some public health experts who reviewed the CDC document said they are now even more worried about the Delta variant, which was first detected in India in December and has since spread to more than 100 countries. The U.S. is currently averaging around 71,000 new coronavirus cases a day, with more than 80% of those attributable to the Delta strain.

"I finished reading it significantly more concerned than when I began," Robert Wachter, chairman of the Department of Medicine at the University of California at San Francisco, told the Post.

But Dr. Ashish Jha, dean of the Brown University School of Public Health, said that while the document makes clear the Delta variant is a major issue, he found the presentation to be "largely reassuring."

"Bottom line? Yeah, Delta variant is bad. Like really bad," Jha wrote in a series of tweets late Thursday. But, he added: "Our vaccines are good. Like really good. Breakthrough infections happen, sometimes they may spread to others. But if enough people get the shot, the pandemic does come to an end."

In addition to full vaccination, the CDC document recommends "universal masking" as a way to control the spread of the Delta variant. That advice is significantly more sweeping than the guidance the CDC released to the public earlier this week, which recommended that vaccinated people wear masks in public indoor spaces only in areas of the country where cases are surging.

The agency's presentation surfaced as President Joe Biden announced Thursday that federal civilian employees who do not show proof of vaccination will be required to wear a mask, undergo coronavirus testing once or twice per week, and socially distance. The president also vowed to "continue to do everything I can to encourage the unvaccinated to get vaccinated."

"Last month, a study showed that over 99% of Covid-19 deaths had been among the unvaccinated—99%," Biden said in a speech Thursday. "People are dying and will die who don't have to die. If you're out there unvaccinated, you don't have to die."


Our work is licensed under Creative Commons (CC BY-NC-ND 3.0). Feel free to republish and share widely.

This is the world we live in. This is the world we cover.

Because of people like you, another world is possible. There are many battles to be won, but we will battle them together—all of us. Common Dreams is not your normal news site. We don't survive on clicks. We don't want advertising dollars. We want the world to be a better place. But we can't do it alone. It doesn't work that way. We need you. If you can help today—because every gift of every size matters—please do. Without Your Support We Simply Don't Exist.

Sunrise Movement Warns of 'Betrayal' as Pelosi Bends Toward Corporate Democrats

"We need Dems to hold the line for a $3.5 trillion reconciliation bill, full stop."

Jake Johnson ·


Progressive Groups Warn Congress Against Including Carbon Tax in Reconciliation Package

"If lawmakers are really concerned about holding the costs of this spending bill, they should get rid of the billions of dollars we waste every year on subsidies to polluters."

Jessica Corbett ·


Opposing His Renomination, Warren Calls Fed Chair Powell 'A Dangerous Man'

"Your record gives me grave concern," Sen. Elizabeth Warren told Jerome Powell. "Over and over, you have acted to make our banking system less safe."

Jake Johnson ·


California Wildfire Victims Lead Calls for Tougher PG&E Criminal Penalties

"The power company is the biggest serial killer in state history, and all it gets is fines?"

Brett Wilkins ·


Progressives Warn Democrats Against Means-Testing Reconciliation Bill to Death

"Raising taxes on the rich is much more efficient than means-testing benefits and accomplishes exactly what the spending hawks claim to be concerned about!"

Kenny Stancil ·

Support our work.

We are independent, non-profit, advertising-free and 100% reader supported.

Subscribe to our newsletter.

Quality journalism. Progressive values.
Direct to your inbox.

Subscribe to our Newsletter.


Common Dreams, Inc. Founded 1997. Registered 501(c3) Non-Profit | Privacy Policy
Common Dreams Logo