The CDC warned House lawmakers Thursday that the new 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, according to a copy of the document reviewed by CNBC and authenticated by the U.S. 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, and MERS and SARS, two diseases also caused by coronaviruses, according to the document. Only measles appears to spread faster than the variant.
“The war has changed,” CDC officials 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. At the current rate, there are 35,000 symptomatic infections per week among 162 million vaccinated Americans, according to the document.
Separately, the CDC has said that 5,914 fully vaccinated people have been hospitalized or 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 congregate settings, 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 Centers for Disease Control and Prevention 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.
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 studies in Canada, Singapore and Scotland that showed higher odds of hospitalization, ICU admission, oxygen needs, pneumonia or death among people infected with the delta variant.
While the delta variant 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, 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.