The Delta variant of COVID-19 may cause more severe illness than all other forms of the virus and infect people as easily as chickenpox, the Centre for Disease Control and Prevention of the US has said in an unpublished document.
The report, contents of which were first reported by The Washington Post on Thursday, said that vaccinated people may spread the Delta variant at the same rate as unvaccinated individuals.
The Delta variant, originally known as B.1.617.2, was first discovered in India and accounts for 80 per cent of the total cases. It has been detected in at least 90 countries.
Dr Rochelle P Walensky, the director of the CDC, acknowledged on Tuesday that vaccinated people with so-called breakthrough infections of the Delta variant carry just as much virus in the nose and throat as unvaccinated people and may spread it just as readily, if less often.
The internal document says the variant is more transmissible than the viruses that cause MERS, SARS, Ebola, the common cold, the seasonal flu and smallpox, and it is as contagious as chickenpox.
The document calls upon the US health agency to acknowledge the fact that “the war has changed”. The document’s tone reflects alarm among CDC scientists about Delta’s spread across the country, the New York Times quoted a federal official, who has seen the research described in the document, as saying.
The agency was expected to publish additional data on the deadly variant on Friday.
“The CDC is very concerned with the data coming in that Delta is a very serious threat that requires action now,” the official said.
There are roughly 35,000 symptomatic infections per week among 162 million vaccinated Americans, according to data collected by the CDC as of July 24 that was cited in the internal presentation. But the agency does not track all mild or asymptomatic infections, so the actual incidence may be higher.
The document said that infection with the Delta variant produces virus amounts in the airways that are tenfold higher than what is seen in people infected with the Alpha variant, which is also highly contagious.
The amount of virus in a person infected with Delta is a thousandfold more than what is seen in people infected with the original version of the virus, a recent study has said.
The CDC document relies on data from multiple studies, including an analysis of a recent outbreak in Provincetown, Massachusetts, which began after the town’s Fourth of July festivities.
Walensky told CNN that the Delta variant “is one of the most transmissible viruses we know about. Measles, chickenpox, this – they’re all up there.” She advised everyone in schools – students, staff and visitors – to wear masks at all times.
“The measures we need to get this under control – they’re extreme. The measures you need are extreme,” Walensky said.
“The bottom line was that, in contrast to the other variants, vaccinated people, even if they didn’t get sick, got infected and shed virus at similar levels as unvaccinated people who got infected,” Walter Orenstein, who heads the Emory Vaccine Center and who viewed the documents, told CNN.
The document, however, said that vaccinated people are safer than unvaccinated ones. “Vaccines prevent more than 90 per cent of severe disease, but may be less effective at preventing infection or transmission,” it said. “Therefore, more breakthrough and more community spread despite vaccination,” the document added.
(With inputs from agencies)