The Centers for Disease Control and Prevention issued a stern warning regarding the delta variant of the coronavirus: “Recognize that the war has changed. Now he says even people who have been vaccinated are able to easily spread the virus.
That’s part of the message of 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 United States. The document, obtained by NBC News on Friday and first published by the Washington Post, explains the scientific background behind the agency’s change in mask guidelines earlier this week.
He concludes that the delta variant is “very contagious, likely to be more serious” and that “breakthrough infections can be as transmissible as unvaccinated cases”.
The researchers focused on viral load – a term for the amount of virus in the bodies of infected people – which can affect transmissibility and severity. Infections with the delta variant cause higher levels of the virus in the body, even in breakthrough cases in fully vaccinated individuals, according to the document. Virus levels can be as high in breakthrough cases as in unvaccinated people, although vaccinated people do not get as sick.
Additionally, these higher levels also persist longer than those seen with previous strains, meaning an infected person is likely contagious for longer.
Yet epidemics mostly occur in unvaccinated people, according to CDC director Dr. Rochelle Walensky.
“I think we are still largely in an unvaccinated pandemic,” Walensky said Tuesday during a press briefing to announce updated guidelines on wearing masks. “The vast majority of transmission, the vast majority of serious illnesses, hospitalizations and deaths occur almost exclusively in unvaccinated people. “
Vaccines continue to be effective, especially in preventing serious illness, according to the document. But they may not be as effective at preventing infection or transmission of the delta variant.
This is a change from the previous variants. The vaccines have been very effective in preventing transmission of the alpha variant, which was the dominant strain in the country earlier this year when the CDC first declared that those vaccinated did not need to wear masks.
“As a result, more breakthroughs and more community spread despite vaccination,” the document said.
Dr Ashish Jha, Dean of Brown University School of Public Health, tweeted Thursday evening that the CDC’s presentation was “insightful and largely reassuring,” noting that data shows the delta variant is highly contagious but vaccines continue to prevent most infections and almost all hospitalizations.
The document notes that the risk of infection is three times lower in those vaccinated and that the risk of serious illness or death is at least ten times lower in those vaccinated.
The paper also provided more concrete figures 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 United States. The agency stopped providing public information on most breakthrough infections in April, when the count hit 10,000. As of that point, the CDC’s website has only released data on revolutionary infections that led to hospitalization or death.
It also details how the delta variant is more contagious than previous versions of the coronavirus. A table included in the document states that it is more transmissible than the flu, colds and even smallpox and is comparable to chickenpox, considered one of the most contagious common viruses.
The document comes as the United States grapples with an increase in coronavirus cases, especially in areas where vaccination rates remain low. Parts of Missouri and Louisiana have reported an increase in hospitalizations comparable to the worst days of the pandemic. Daily deaths in the United States have risen steadily in recent weeks, but remain significantly lower than in the spring.
Jason abbruzzese contributed.