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Internal CDC document warns 'the war has changed' with the more infectious Delta variant: Washington Post

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The blue-and-white CDC sign in front of the agency's Atlanta headquarters at sunset
The Centers for Disease Control and Prevention's headquarters in Atlanta. Tami Chappell/Reuters

The Delta coronavirus variant spreads more easily than the viruses that cause Ebola, the common cold, and smallpox, according to an internal presentation from the US Centers for Disease Control and Prevention obtained by The Washington Post.

Each person infected with Delta may spread the coronavirus to 5 to 9.5 others, on average, according a chart included in the presentation. That makes Delta roughly as contagious as chickenpox, and far more infectious than the original coronavirus strain, which allowed each person to pass the virus to 1.5 to 3.5 others, on average.

The presentation also noted that people who are fully vaccinated could spread Delta just as easily as those who are unvaccinated, based on unpublished data recently collected from outbreak investigations and studies.

The CDC must now "acknowledge that the war has changed," one slide said.

The agency recommended Tuesday that everyone, including those who have been fully vaccinated, wear masks indoors in regions where COVID-19 is spreading quickly - a reversal from its policy in May, when the CDC said masks were no longer necessary for those who had received their shots.

President Joe Biden also announced Thursday that all federal employees will be required to get vaccinated, or be tested regularly for COVID-19 and wear a mask. The mandate came just days after the US Department of Veterans Affairs required healthcare employees to get vaccinated within the next two months.

Several states have announced similar mandates in the last week: California will soon require state employees and healthcare workers to provide proof of vaccination or get tested weekly. New York will ask the same of all state employees by Labor Day.

The new data influenced the CDC's mask guidance

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CDC Director Rochelle Walensky in Wilmington, Delaware on December 8, 2020. Kevin Lamarque/Reuters

An anonymous federal health official told The Post that data cited in the CDC slideshow played a key role in the agency's decision to recommend masks again.

"Although it's rare, we believe that at an individual level, vaccinated people may spread the virus, which is why we updated our recommendation," the official said. "Waiting even days to publish the data could result in needless suffering, and as public-health professionals, we cannot accept that."

Already, average daily COVID-19 cases in the US have risen nearly sixfold in the last month, from around 12,000 to 72,000 per day. Hospitalizations, too, have more than doubled in that time, from around 17,000 to 38,000 per day, on average.

The CDC presentation said Delta's symptoms were probably more severe than those of earlier coronavirus variants. It cited reports in Canada and Scotland, where people infected by the variant had higher chances of needing hospitalization, and Singapore, where Delta infections have produced an increased demand for oxygen and intensive-care admissions.

But the current vaccines remain highly effective at preventing severe illness, hospitalization, or death.

The presentation said the CDC needed to amp up its messaging of the vaccine's efficacy and usefulness in mitigating the pandemic. It also suggested considering both vaccine and mask mandates to protect those especially vulnerable to the virus and to control the pandemic's spread.

Vaccines still do a great job of preventing severe disease and death

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Maryland National Guard Specialist James Truong (right) administers a Moderna coronavirus vaccine at CASA de Maryland's Wheaton Welcome Center in Wheaton, Maryland on May 21, 2021. Chip Somodevilla/Getty Images

Delta seems to have challenged how well vaccines work at preventing infection or transmission.

Two doses of Pfizer's or Moderna's vaccine were initially shown to reduce the risk of getting COVID-19 by 95% in clinical trials. However, a study in the New England Journal of Medicine recently found that Pfizer's two-dose vaccine reduces the risk of a symptomatic Delta infection by just 88%. That increases the odds that fully vaccinated people will get COVID-19 - what's known as a "breakthrough case."

Breakthrough cases are still rare, according to the CDC, but they become more common as vaccine coverage increases. The agency is currently recording around 35,000 symptomatic COVID-19 cases per week among 162 million vaccinated Americans - a rate of just 0.2%. (That data may be limited, though, since the CDC stopped tracking asymptomatic, mild, or moderate breakthrough cases at a national level in May.)

Still, vaccines reduce the risk of getting COVID-19 by eightfold, and reduce the risk of hospitalization or death by 25-fold, the CDC presentation said.

One slide noted, however, that older people have a higher risk of hospitalization and death from COVID-19, regardless of their vaccination status.

Vaccines also seem to be less effective for immunocompromised people: One study cited in the presentation found that mRNA vaccines such as Pfizer's or Moderna's reduce the risk of hospitalization by 59% for immunocompromised people, compared with 91% for people who aren't in that category.

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