Leaked CDC Data Causes Concern About Breakthrough Infections

This new data shows why the CDC is recommending masks even for vaccinated individuals.

As the Delta variant continues to spread, rapidly infecting unvaccinated people and causing some breakthrough infections in those who have been vaccinated, the Centers for Disease Control and Prevention (CDC) suddenly altered its guidance on wearing masks. Many people were surprised by the update, since the agency did not release any corresponding data to support the change. Now, The Washington Post has published leaked data from the CDC that an official says led the agency to change their advice on mask-wearing. The data shows that while vaccines continue to be highly effective, there is reason to be concerned.

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On July 29, The Washington Post shared slides from an internal CDC meeting earlier in the day. The CDC has yet to comment on the data, but an anonymous federal health official told The Washington Post that the data cited in the slides played an essential role in the CDC's decision to update its mask guidelines. The guidance now suggests that everyone, vaccinated or not, wear masks indoors in public in areas that have high transmission of the virus.

Experts agree that the data within the leaked slides gives good reason for us to return to wearing masks in certain high-risk settings. "The data makes a pretty compelling justification for why we need to go back to mask-wearing and other public health measures," Charles Chiu, PhD, an infectious disease specialist at the University of California, told USA Today. "I do think it's because of the Delta variant."

The Delta variant is highly contagious, which makes the return of masks pertinent. The CDC data notes that the variant is more transmissible than severe acute respiratory syndrome (SARS), Ebola, the common cold, the Spanish flu, and smallpox. It's about as transmissible as the infamously contagious chickenpox.

The vaccines continue to prove effective in preventing severe disease from the Delta variant. The data shows that the vaccines approved for use in the U.S. prevent more than 90 percent of severe disease. However, the CDC does note that the vaccines may be less effective than this when it comes to preventing infection or transmission of the Delta variant. "Therefore, [there is] breakthrough and more community spread despite vaccination" as the Delta variant makes its rounds. According to the data, "breakthrough infections may be as transmissible as unvaccinated cases."

John Moore, a virologist at Weill Cornell Medicine summed up the CDC's data succinctly for The New York Times. "Overall, Delta is the troubling variant we already knew it was," Moore told the newspaper. "But the sky isn't falling and vaccination still protects strongly against the worse outcomes."

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The CDC has alluded to some of this data before. On July 27, during a press briefing, CDC director Rochelle Walensky, MD, said, "I have seen new scientific data from recent outbreak investigations showing that the Delta variant behaves uniquely differently from past strains of the virus that cause COVID-19." She explained that some vaccinated people who get the Delta variant can be contagious and spread the virus. "This new science is worrisome and unfortunately warrants an update to our recommendations," Walensky added.

In the leaked slides, the CDC notes its concern about the public's response to breakthrough infections. The slides say that as cases increase, it becomes increasingly more challenging to communicate positively with the public, even as vaccine effectiveness in preventing hospitalization and death remains consistent. The agency says that as the caseload grows, local health departments and the public tend to get more concerned that the vaccines don't work or that they will need booster shots.

Matthew Seeger, a risk communication expert at Wayne State University in Detroit, told The Washington Post that a lack of communication about breakthrough infections early on—with officials opting to strictly laud vaccines for their high efficacy—has resulted in these challenges. "We've done a great job of telling the public these are miracle vaccines," Seeger said. "We have probably fallen a little into the trap of over-reassurance, which is one of the challenges of any crisis communication circumstance."

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