The Centers for Disease Control and Prevention has issued a stern warning about the delta variant of the coronavirus: "Acknowledge the war has changed." Now, even vaccinated people are able to readily spread the virus.
That is part of the message from a recent internal presentation prepared by the CDC detailing the dangers posed by the delta variant, which has already led to a spike in cases in the U.S. The document, obtained Friday by NBC News and first published by The Washington Post, explains the scientific background behind the agency’s change in mask guidance earlier this week.
It concludes that the delta variant of the coronavirus is “highly contagious, likely to be more severe” and that “breakthrough infections may be as transmissible as unvaccinated cases.”
Infections with the delta variant lead to higher levels of virus in the body, even in breakthrough cases in fully vaccinated individuals, the document said. Virus levels can be as high in breakthrough cases as in unvaccinated people, even if vaccinated people don’t get nearly as sick. What’s more, these higher levels also persist for longer than was seen with previous strains, meaning an infected person is likely contagious for longer.
Vaccines continue to be effective, particularly at preventing severe disease, according to the document. But they may not be as good at preventing infection or transmission of the delta variant.
That’s a change from previous variants. The vaccines were very effective at preventing transmission of the alpha variant, which was the dominant strain in the country earlier this year when the CDC first said that vaccinated people do not need to wear masks.
"Therefore, more breakthrough and more community spread despite vaccination," the document states.
Dr. Ashish Jha, dean of the Brown University School of Public Health, tweeted Thursday night that the CDC presentation was "insightful & largely reassuring," emphasizing that the data shows the delta variant is highly contagious but the vaccines continue to prevent most infections and almost all hospitalizations.
The document also provided more concrete numbers on breakthrough infections, estimating that at current levels, there are 35,000 symptomatic breakthrough infections per week among the 162 million fully vaccinated adults in the U.S. The agency stopped providing public information on most breakthrough infections in April, when the tally hit 10,000. From that point on, the CDC website only posted data on breakthrough infections that led to hospitalization or death.
This story was originally published on NBC News.