Internal CDC Document Says Delta Variant May Be as Contagious as Chickenpox

But the vaccines remain highly effective at preventing severe illness.

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The Delta variant may be as contagious as the chickenpox and likely leads to more severe illness than earlier variants of COVID-19, according to an internal Centers for Disease Control and Prevention presentation obtained by the Washington Post.

The presentation, which helped inform the CDC’s decision earlier this week to recommend a return to indoor mask wearing in areas with high rates of transmission, presents a concerning overview of vaccinated people’s ability to contract and spread the Delta variant. But it also makes clear that vaccination is still the best way to prevent severe illness and death from COVID-19.

It’s a tricky combination to message. The CDC has to explain that the vaccines are far from perfect when it comes to preventing breakthrough infections, while still encouraging unvaccinated Americans to get their shots.

Overall, the CDC estimates that vaccinated Americans are about 25 times less likely to be hospitalized or die from COVID-19 than those who aren’t vaccinated. 

CDC

Between April and May, however, the share of people who died of COVID-19 in hospitals who were vaccinated jumped from 3.1 percent to 15.1 percent, according to the slideshow.

CDC

The CDC’s modeling suggests that Delta is roughly as contagious as chickenpox, while also being far more deadly. One slide shows that each person infected with the Delta variant infects at least 5 people on average, compared to a little more than 1 for the ancestral strain identified early in the pandemic.

CDC

The CDC also cites data showing that vaccinated people who get breakthrough infections carry much higher viral loads relative to earlier variants. Based on that, it concludes that the “Delta variant vaccine breakthrough cases may be as transmissible as unvaccinated cases.”

Along with being more contagious, the Delta variant appears to lead to higher odds of hospitalization and severe illness, according to data from Canada, Scotland, and Singapore. 

Despite those warning signs, the presentation shows that Pfizer’s vaccine remains highly effective at preventing hospitalization and death when someone is infected with the Delta variant. Overall, the CDC estimates that the vaccines prevent severe illness more than 90 percent of the time.    

CDC

In response to the new data, the unnamed authors of the presentation recommended, among other measures: universal masking, improved communication about the potential for breakthrough infections, and, potentially, vaccinate mandates. 

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