An internal CDC document obtained by multiple media outlets suggests that vaccinated people who are infected with the delta variant carry just as high a viral load as unvaccinated people, and that the variant is more contagious than many other common viruses.

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Details on the documents

According to the Washington Post, the document is an internal CDC presentation that incorporates both published and unpublished data, with a particular focus on the delta variant. The findings and conclusions are reportedly those of the authors, rather than the agency as a whole.

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The presentation strikes "an urgent note," according to the Post, describing "a variant so contagious that it acts almost like a different novel virus."

Specifically, the document suggests the delta variant is more contagious than the viruses that cause MERS, SARS, the common cold, influenza, and smallpox, and is just as contagious as chickenpox, the New York Times reports.

The document also pointed to three studies, two of which have yet to be peer-reviewed, that showed patients who contracted the delta variant were more likely to be hospitalized, be admitted to the ICU, or die than those who were infected with other variants of the virus.

Another analysis in the document examined a recent outbreak of 882 cases in Provincetown, Mass., caused by the delta variant. It found that 74% of the infected individuals had been vaccinated, and that vaccinated and unvaccinated people carried similarly large viral loads in their noses and throats.

The document also indicated that those infected with the delta variant have viral loads in their airways tenfold higher than seen in those infected with the alpha variant. An earlier study had showed that, at the time of their first positive test, those infected with the delta variant carry viral loads a thousandfold higher than those infected with the original strain of the virus.

One slide in the document showed that risk of hospitalization and death from Covid-19 remains higher among older age groups than younger groups, regardless of vaccination status, the Washington Post reports.

The document also suggested the delta variant can, in some cases, reinfect people who have already had Covid-19. Specifically, among those who had recovered from Covid-19 at least 180 days earlier, the risk of infection with the delta variant was around 46% higher than infection with the alpha variant.

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'The war has changed'

In the document, CDC acknowledged the "communication challenges" it has faced regarding Covid-19 cases among vaccinated people.

The next step for CDC is to "acknowledge the war has changed," the document said, and added that CDC needs to "improve communications around individual risk among [the] vaccinated."

Matthew Seeger, a risk communication expert at Wayne State University, said poor communication about breakthrough infections has been a problem.

"We've done a great job of telling the public these are miracle vaccines," he said. "We have probably fallen a little into the trap of over-reassurance, which is one of the challenges of any crisis communication circumstance."

According to a CDC official who spoke to the Times on condition of anonymity, the agency "is very concerned with the data coming in that delta is a very serious threat that requires action now."

Current CDC guidelines say people in areas of high transmission of the coronavirus should wear masks indoors, regardless of vaccination status. The internal document, however, suggested even stronger guidance. "Given higher transmissibility and current vaccine coverage, universal masking is essential," the documents said.

Outside experts were troubled by the presentation's findings. Robert Wachter, chair of the Department of Medicine at the University of California-San Francisco, said, "I finished reading it significantly more concerned than when I began."

But John Moore, a virologist at Weill Cornell Medicine, argued the presentation didn't reveal a fundamental change in the epidemic. "Overall, delta is the troubling variant we already knew it was," he said. "But the sky isn't falling, and vaccination still protects strongly against the worse outcomes." (Mandavilli, New York Times, 7/30; Abutaleb et al., Washington Post, 7/29; Kaplan, Los Angeles Times, 7/30; Weintraub, USA Today, 7/30; Anthes, New York Times, 7/28; Gonzalez, Axios, 7/28)