The Delta coronavirus variant spreads more easily than the viruses that cause Ebola, the
, and smallpox, according to an internal presentation from the Centers for Disease Control and Prevention, which was first obtained by The Washington Post.
Each person infected with Delta may spread the coronavirus to between 5 and 9.5 others, on average, according a chart in the presentation. That makes Delta roughly as contagious as chickenpox, and far more infectious than the original coronavirus strain, which infected people pass on to between 1.5 and 3.5 others, on average.
The presentation also noted that people who are fully vaccinated can spread Delta as easily as those who are unvaccinated, based on unpublished data collected from outbreak investigations.
The CDC must “acknowledge that the war has changed,” one slide said.
The agency recommended on 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’d gotten their shots.
President Joe Biden also announced on Thursday that all federal employees will be required to get vaccinated, or be tested regularly for COVID-19 and wear a mask. A few days prior, the Department of Veterans Affairs also said it will require healthcare employees to get vaccinated within the next two months.
Several states have announced similar mandates: 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.
New data influenced the CDC’s mask guidance
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.”
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 from Canada and Scotland, which found that people infected by the variant had a higher chance of hospitalization, and from Singapore, where Delta infections have produced an increased demand for oxygen and ICU admissions.
But vaccines remain highly effective at preventing severe illness, hospitalization, or death.
The presentation said the CDC needed to amp up its messaging of the vaccines’ efficacy and usefulness in mitigating the pandemic. It also suggested considering both vaccine and mask mandates to protect vulnerable people and to control the virus’ spread.
Vaccines prevent severe disease and death
Delta seems to have challenged how well vaccines prevent infection and 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 88%. That means more fully vaccinated people could get COVID-19 — what’s known as a “breakthrough case.”
Breakthrough cases are still rare, though. The CDC 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.)
Vaccines reduce the risk of getting COVID-19 eight-fold, and reduce the risk of hospitalization or death 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 Pfizer’s or Moderna’s mRNA vaccines 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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