In-Depth: What an internal CDC document reveals about the delta variant

COVID-19 transmission delta variant
Posted at 6:30 PM, Jul 30, 2021
and last updated 2021-07-30 21:47:54-04

SAN DIEGO (KGTV) -- The delta variant is far more contagious than previous versions of COVID and likely more severe, according to a sobering new assessment in an internal document from the Centers for Disease Control and Prevention.

While vaccines remain more than 90 percent effective against hospitalization from delta, outbreak investigations reveal the variant can still cause mild breakthrough infections and leap from one vaccinated person to another, the document says.

Vaccinated people who are sickened with delta appear to be able to spread it as efficiently as the unvaccinated, although the vaccinated have an 8 times lower chance of getting infected in the first place, according to the CDC document.

The internal CDC briefing presentation is dated July 29. It was first obtained by the Washington Post.

This week, the agency updated its health guidelines to urge all Americans to wear masks indoors regardless of vaccination status.

“It does convince me that wearing your mask indoors is the right thing to do right now to protect folks, especially the immunocompromised and children who can’t get vaccinated,” said Dr. Navaz Karanjia of UC San Diego Health. “These data show that the war against COVID has gotten harder because the enemy has gotten smarter.”

The document hints that further public health interventions may be necessary to combat the variant.

Delta is several times more contagious than the common cold, the seasonal flu, and the original form of SARS-CoV-2, the document says. Every person with delta will spread it to five to ten others, on par with how fast chickenpox spreads.

The original form of SARS-CoV-2 spread to two to three others.

In some cases, vaccinated people can spread the virus as efficiently as the unvaccinated. That’s based on data from places like Provincetown, Mass. in Cape Cod. During the town’s boisterous Fourth of July party scene, there was an outbreak that sickened nearly 900 people.

The CDC released a detailed analysis Friday of some of the cases. During a two-week period, 469 people were infected with COVID even though 74 percent were vaccinated.

Of those cases, 274 vaccinated people wound up getting symptoms, but only four vaccinated people were sick enough to go to the hospital. Two of the four had underlying conditions; all survived.

“If you do get infected and get symptomatic with the delta variant, then you are able to transmit it to other people about as easily as people who are unvaccinated,” Dr. Karanjia said. “But remember, the number of people that are going to get infected and symptomatic if they’re vaccinated is much lower.”

The risk of hospitalization is 25 times lower for the vaccinated, the document says.