The Delta variant of the Covid-19 may cause more severe sickness than all other known variants of the virus and spread as easily as chickenpox, reports said.

The document from the Centers for Disease Control and Prevention (CDC) outlines unpublished data that shows fully vaccinated people might spread the Delta variant, first identified in India, at the same rate as unvaccinated people, reports said.

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The contents of the document – a slide presentation – were first reported by The Washington Post on Thursday.

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.

According to The New York Times, 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.

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Here are the top points about the Delta variant of COVID-19:

The Delta variant — originally known as B.1.617.2 — might cause more severe disease, according to the document.

The immediate next step for the agency is to acknowledge the war has changed, the document said.

The document’s tone reflects alarm among CDC scientists about Delta’s spread across the country; the NYT quoted a federal official as saying.

The agency is 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.

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 thousand-fold 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.