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COVID-19 | US CDC internal report calls Delta variant as contagious as chickenpox

The CDC's new masking guidelines for vaccinated people, introduced Tuesday, were based on the information presented in the document.

July 30, 2021 / 11:11 AM IST
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 document noted.

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 document noted.

The delta variant is much more contagious, more likely to break through protections afforded by the vaccines and may cause more severe disease than all other known versions of the virus, according to an internal presentation circulated within the Centers for Disease Control and Prevention.

Dr. Rochelle Walensky, the director of the agency, acknowledged Tuesday that vaccinated people with so-called breakthrough infections of the delta variant carry just as much virus in their nose and throat as unvaccinated people, and may spread it just as readily, if less often.

But the internal document lays out a broader and grimmer view of the variant.

The delta 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, according to the document, a copy of which was obtained by The New York Times.

The immediate next step for the agency is to “acknowledge the war has changed,” the document said. Its contents were first reported by The Washington Post on Thursday evening.

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A vaccine works by mimicking a natural infection. A vaccine not only induces immune response to protect people from any future COVID-19 infection, but also helps quickly build herd immunity to put an end to the pandemic. Herd immunity occurs when a sufficient percentage of a population becomes immune to a disease, making the spread of disease from person to person unlikely. The good news is that SARS-CoV-2 virus has been fairly stable, which increases the viability of a vaccine.

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There are broadly four types of vaccine — one, a vaccine based on the whole virus (this could be either inactivated, or an attenuated [weakened] virus vaccine); two, a non-replicating viral vector vaccine that uses a benign virus as vector that carries the antigen of SARS-CoV; three, nucleic-acid vaccines that have genetic material like DNA and RNA of antigens like spike protein given to a person, helping human cells decode genetic material and produce the vaccine; and four, protein subunit vaccine wherein the recombinant proteins of SARS-COV-2 along with an adjuvant (booster) is given as a vaccine.

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Vaccine development is a long, complex process. Unlike drugs that are given to people with a diseased, vaccines are given to healthy people and also vulnerable sections such as children, pregnant women and the elderly. So rigorous tests are compulsory. History says that the fastest time it took to develop a vaccine is five years, but it usually takes double or sometimes triple that time.

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The document’s tone reflects alarm among CDC scientists about Delta’s spread across the country, said a federal official who has seen the research described in the document. The agency is expected to publish additional data on the variant 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 were 71,000 new cases per day on average in the United States, as of Thursday. The new data suggest that vaccinated people are spreading the virus and contributing to those numbers — although probably to a far lesser degree than the unvaccinated.

Walensky has called transmission by vaccinated people a rare event, but other scientists have suggested it may be more common than once thought.

The agency’s new masking guidelines for vaccinated people, introduced Tuesday, were based on the information presented in the document. The CDC recommended that vaccinated people wear masks indoors in public settings in communities with high transmission of the virus.

But the internal document hints that even that recommendation may not go far enough. “Given higher transmissibility and current vaccine coverage, universal masking is essential,” the document said.

The agency’s data suggest that people with weak immune systems should wear masks even in places that do not have high transmission of the virus. So should vaccinated Americans who are in contact with young children, older adults, or otherwise vulnerable people.

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.

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 document noted.

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, according to one recent study.

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. By Thursday, that cluster had grown to 882 cases. About 74% were vaccinated, local health officials have said.

Detailed analysis of the spread of cases showed that people infected with delta carry enormous amounts of virus in their nose and throat, regardless of vaccination status, according to the CDC document.

“This is one of the most impressive examples of citizen science I have seen,” said Dr. Celine Gounder, an infectious disease specialist at Bellevue Hospital Center in New York. “The people involved in the Provincetown outbreak were meticulous in making lists of their contacts and exposures.”

Infection with the delta variant may be more likely to lead to severe illness, the document noted. Studies from Canada and Scotland found that people infected with the variant are more likely to be hospitalized, while research in Singapore indicated that they are more likely to require oxygen.

Still, the CDC’s figures show that the vaccines are highly effective in preventing serious illness, hospitalization and death in vaccinated people, experts said.

“Overall, delta is the troubling variant we already knew it was,” said John Moore, a virologist at Weill Cornell Medicine in New York. “But the sky isn’t falling and vaccination still protects strongly against the worse outcomes.”

By Apoorva Mandavilli

c.2021 The New York Times Company
New York Times
first published: Jul 30, 2021 11:08 am

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