- The CDC warned the delta variant sweeping across the country is as contagious as chickenpox, has a longer transmission window than the original Covid-19 strain and may make older people sicker.
- A confidential CDC document said delta is more transmissible than the common cold, the 1918 Spanish flu, smallpox, Ebola, MERS and SARS.
- Health officials said federal and state leaders should communicate to the public the benefits of getting vaccinated.
The CDC warned House lawmakers that the delta variant sweeping across the country is as contagious as chickenpox, has a longer transmission window than the original Covid-19 strain and may make older people sicker, even if they've been fully vaccinated.
The warning on Thursday was made in a confidential document that was reviewed by CNBC and authenticated by the federal health agency.
Delta, now in at least 132 countries and already the dominant form of the disease in the United States, is more transmissible than the common cold, the 1918 Spanish flu, smallpox, Ebola, MERS and SARS, according to the document. Only measles appears to spread faster than the variant.
"The war has changed," officials of the Centers for Disease Control and Prevention wrote.
Health officials said federal and state leaders should communicate to the public the benefits of getting vaccinated, adding the Covid vaccine shots reduce the risk of severe disease and death "10-fold or greater" and reduce the risk of infection "3-fold."
Vaccines prevent more than 90% of severe disease, but may be less effective at preventing infection, they said, making community spread among the vaccinated more likely. The document said 35,000 symptomatic infections are occurring per week among 162 million vaccinated Americans.
Separately, the CDC has said 5,914 fully vaccinated people have been hospitalized or have died with Covid infections as of July 19, the most recent data available. Breakthrough cases, which occur in the fully vaccinated, happen more frequently in gatherings of people and in groups at risk of primary vaccine failure, according to the document.
Health officials also said federal and state leaders should consider vaccine mandates, particularly for health-care workers, universal masking and other community mitigation strategies. President Joe Biden announced on Thursday his administration would require federal workers to prove their vaccination status or submit to a series of rigorous safety protocols.
The documents presented to lawmakers came two days after the CDC reversed course on its prior guidance and recommended fully vaccinated Americans who live in areas with high Covid infection rates resume wearing face masks indoors. The guidelines cover about two-thirds of the U.S. population, according to a CNBC analysis.
"My first thoughts in reading it was that everything is a little bit worse than I thought," said Dr. Robert Wachter, chairman of the Department of Medicine at the University of California at San Francisco, who reviewed the document.
"This document and some of the other information says you've got to be open to the possibility that delta is worse in a number of ways and may upend some of our prior assumptions in ways that are meaningful," he said.
Dr. Paul Offit, who advises the FDA on Covid vaccines, said Friday it is "profoundly" upsetting that the U.S. hasn't gotten a critical portion of the population vaccinated, adding delta has "changed the game." About half of the U.S. population is fully vaccinated, according to CDC data.
"Yesterday, you had 90,000 cases and close to 400 deaths," Offit said. "Those are same numbers you saw last summer. I mean, last summer, you had a fully susceptible population and you had no vaccine."
He said the CDC documents highlight just how "frustrated" federal officials are, given that there are safe and effective vaccines.
"The war isn't against the virus anymore. It's also at some level a war against ourselves," he said.
People infected with the delta variant carry up to 1,000 times more virus in their nasal passages than other strains, resulting in higher transmissibility, even among the vaccinated, according to federal health officials. The CDC noted that studies in Canada, Singapore and Scotland found higher odds of hospitalization, ICU admission, oxygen needs, pneumonia or death among people infected with the delta variant.
While the variant, which surfaced in India, continues to hit unvaccinated people the hardest, some vaccinated people could be carrying higher levels of the virus than previously understood and are potentially transmitting it to others, CDC Director Dr. Rochelle Walensky said Tuesday. She added the variant behaves "uniquely differently from past strains of the virus."
"This pandemic continues to pose a serious threat to the health of all Americans," Walensky told reporters on a call.
Rep. James E. Clyburn, D-S.C., chairman of the Select Subcommittee on the Coronavirus Crisis, said Walensky and White House chief medical advisor Dr. Anthony Fauci briefed the committee on the new data Thursday.
"I am deeply concerned about the rapidly increasing rates of coronavirus infections in states around the country that is being driven by the Delta variant," Clyburn said in a statement, noting that Covid cases have increased by 145% in the last two weeks and hospitalizations and deaths are rising again, particularly in areas with low vaccination rates. "This sudden turn of events threatens to undermine the significant progress we have made this year to overcome the pandemic."
–CNBC's Rich Mendez, Robert Towey and Nate Rattner contributed to this report.