CDC Internal Report States Covid-19 Delta Variant Is as Contagious as Chickenpox

Both vaccinated and unvaccinated people should wear masks indoors in high transmission areas, which accounts for half the country, according to the agency

A photo of a woman holding a small child in her arms. Both are wearing masks.
Previously, in May, when coronavirus cases were dropping significantly, and vaccination rates were on the rise, the CDC announced that fully vaccinated people could stop masking indoors and outdoors. Nik Anderson via Wikicommons under CC BY 2.0

On July 27, the Centers for Disease Control and Prevention (CDC) revised their guidance on wearing face masks. The health protection agency now recommends that fully vaccinated people return to wearing masks indoors in regions of the United States where Covid-19 infection rates are escalating due to the highly transmissible Delta variant, reports Mike Stobbe for the Associated Press.

The guideline updates result from low vaccination rates in combination with the increased spread and transmissibility of the Covid-19 Delta variant, which accounts for 80 percent of new cases, Jorge L. Ortiz Ryan W. Miller report for USA Today. Less than 50 percent of the United States is fully vaccinated, reports Daniel E. Slotnik, Apoorva Mandavilli, and Sheryl Gay Stolberg for the New York Times.

The updated mask guidelines were put in place ahead of anticipated new data showing the Delta variant’s growing threat. In internal CDC documents obtained by the Washington Post and published Thursday evening, new data suggests the Delta variant “spreads as easily as chickenpox,” report Yasmeen Abutaleb, Carolyn Y. Johnson and Joel Achenbach for the Post. Citing yet-to-be-published data, the CDC presentation suggests vaccinated individuals may be able to spread the Delta variant as easily as unvaccinated people. One slide suggest there have been “35,000 symptomatic infections per week among 162 million vaccinated Americans,” the Post reports.(The CDC presentation is viewable here.)

Previously, in May, when coronavirus cases were dropping significantly, and vaccination rates were on the rise, the CDC announced that fully vaccinated people could stop masking indoors and outdoors, reports Allison Aubrey for NPR. The highest spread of new cases is occurring in areas with low vaccination rates, CDC director Rochelle Walensky tells NPR.

However, more reports of breakthrough infections, or cases where vaccinated individuals become sick with the disease that the vaccine was expected to prevent, caused by the Delta variant are surfacing, reports the New York Times.

"The Delta variant is showing every day its willingness to outsmart us," Walensky tells NPR."When we examine the rare breakthrough infections and we look at the amount of virus in those people, it is pretty similar to the amount of virus in unvaccinated people."

The variant accounts for more than 80 percent of new infections in the U.S., and while vaccines protect against it, breakthrough cases are possible, reports Jorge L. Ortiz and Ryan W. Miller for USA Today.

In general, vaccines effectively control outbreaks, preventing severe illness and hospitalization. Breakthrough cases are expected as no vaccine is 100 percent effective in preventing illness in vaccinated individuals, but these cases are anticipated in only a small percentage of people. As of now, there are no unexpected patterns in vaccine characteristics or case demographics in those who reported a breakthrough infection, per the CDC.

The new CDC guidelines recommend that people should wear masks in locations where more than 50 new infections occur per 100,000 individuals within the previous seven days, or more than eight percent of Covid-19 tests are positive during that time frame in any given location, per the New York Times.

The CDC's COVID Data Tracker shows areas of high transmission rates within U.S. counties. Areas in red have high transmission rates and qualify for masking indoors. States such as Florida, Louisiana, and Arkansas that are shown entirely red on the COVID Data Tracker, for example, should be masking up indoors, reports the New York Times. Currently, 52 percent of the country crosses the CDC’s high risk threshold and should be wearing masks.

The guidelines have been met with some criticism by experts for only requiring masks in areas with high transmission rates.

"The director said the guidance is for people in areas of high transmission, but if you look at the country, every state is seeing a rise in transmission," Ali Mokdad, an epidemiologist and former CDC scientist, tells the New York Times. "So why not say, 'Everybody in the U.S. should be wearing a mask indoors?' The whole country is on fire."