The U.S. Centers for Disease Control and Prevention warns that “the war” against the coronavirus “has changed” in newly reported internal documents evaluating the threat of the delta variant.
“Delta is different than previous strains,” reads a slide in a CDC presentation dated Thursday.
The presentation is circulating within the CDC as the agency considers new public health messaging around vaccine effectiveness and the risk of breakthrough infections in fully vaccinated people. Such cases are still rare, the agency said, and generally not severe, but they are somewhat more likely to happen with the delta variant than with other coronavirus strains.
They offer a clearer picture of why the CDC announced earlier this week that people in certain high-risk areas should resume wearing face masks indoors, even if they are vaccinated, and hint that the agency may be reevaluating other community strategies to mitigate the pandemic, which is now regaining strength in every state.
To put the risk in a more familiar context, the delta variant is as contagious as chickenpox, the agency said. It is more contagious than the common cold, smallpox, Ebola, SARS or MERS.
The good news is that the CDC believes vaccines prevent over 90% of severe illnesses in people who contract the delta variant, according to the internal presentation. Researchers have always understood that some people, particularly the elderly or the immunocompromised, might catch COVID-19, even if they are fully vaccinated. The point is to control the spread, and prevent serious illness and death.
But in breakthrough cases, vaccinated people may be able to transmit the delta variant just as easily as unvaccinated people, the CDC slides say. The suggestion contradicts earlier published studies, conducted before the delta variant became prominent, that have found vaccinated people may transmit significantly less virus than unvaccinated people.
On Friday, the agency highlighted the results of a new study conducted in Barnstable County, Massachusetts, looking at a July COVID-19 outbreak following multiple large public gatherings held indoors and outdoors. Out of nearly 470 infections, around three-quarters occurred in people who had been fully vaccinated. Researchers analyzed samples from 133 of the cases and identified the delta variant in 90% of them.
The infection was not severe in most vaccinated patients; just four required hospitalization, and some had preexisting conditions.
Alex Morse, mayor of Provincetown, Massachusetts ― where the crowded events were held ― said via Twitter that the CDC’s findings represented good news because the vaccines were shown to be working as intended.
The study’s authors noted several limitations, including that “data from this report are insufficient to draw conclusions about the effectiveness of COVID-19 vaccines against SARS-CoV-2, including the Delta variant, during this outbreak.”
Yet in a statement, CDC Director Rochelle Walensky urged caution, saying that the study demonstrates “that Delta infection resulted in similarly high SARS-CoV-2 viral loads in vaccinated and unvaccinated people.”
“This finding is concerning and was a pivotal discovery leading to CDC’s updated mask recommendation,” Walensky said. She went on to note that that the Massachusetts study “is one of many [the] CDC has been involved in across the country and data from those investigations will be rapidly shared with the public when available.”
In its internal presentation, the CDC states that public health messaging surrounding the vaccines has gone awry and suggests what experts should do to encourage more people to get vaccinated and follow safety guidelines ― including helping people better understand breakthrough infections and vaccine effectiveness.
“Acknowledge the war has changed,” reads one bullet point.
As the delta variant spreads, vaccine mandates are being imposed at the federal, state and local levels. California is requiring all health care workers to get their shots following the strong urging of medical professional groups.
Businesses also are joining the trend. Google announced this week that any employee wishing to return to its offices will have to show proof of vaccination.
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