US Covid-19 cases rise as Delta variant spreads

By Meg Wagner, Melissa Macaya, Melissa Mahtani, Veronica Rocha and Fernando Alfonso III, CNN

Updated 8:03 p.m. ET, July 30, 2021
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9:59 a.m. ET, July 30, 2021

A leaked CDC document shows new data on the Delta variant's spread. Here are key things to know.

From CNN's Elizabeth Cohen and Ben Tinker

 Fin Gomez, a journalist with CBS News and White House Correspondents Association board member, replaces signs for mask-wearing guidance around the James Brady Press Briefing Room at the White House on July 27, in Washington, DC.
 Fin Gomez, a journalist with CBS News and White House Correspondents Association board member, replaces signs for mask-wearing guidance around the James Brady Press Briefing Room at the White House on July 27, in Washington, DC. Anna Moneymaker/Getty Images

An internal report presented to the US Centers for Disease Control and Prevention indicates the Delta coronavirus variant is far more transmissible than older lineages, may cause more severe disease, and that when it causes breakthrough infections, may be as easily transmitted as when it infects unvaccinated people.

What the document shows:

  • The slideshow dated Thursday and first obtained by The Washington Post, appears to provide some data backing CDC Director Dr. Rochelle Walensky’s controversial decision on Tuesday to change the agency’s guidance on mask use.
  • It says the Delta variant is about as transmissible as chickenpox, with each infected person, on average, infecting eight or nine others. The original lineage was about as transmissible as the common cold, with each infected person passing the virus to about two other people on average.
  • And if vaccinated people get infected anyway, they have as much virus in their bodies as unvaccinated people. But vaccinated people are safer, the document indicates. It says vaccines reduce the risk of severe disease or death 10-fold and reduce the risk of infection three-fold.
  • The CDC, the document advises, should “acknowledge the war has changed.” It recommends vaccine mandates and universal mask requirements.

How the CDC reacted:

  • Walensky confirmed to CNN that the slideshow was presented to her at a noon briefing on Thursday. “I think people need to understand that we’re not crying wolf here. This is serious,” Walensky told CNN Thursday night. “It’s one of the most transmissible viruses we know about. Measles, chicken pox, this – they’re all up there," she said.
  • Walensky noted that the R0 for the Delta variant – a measure of its transmissibility – is estimated to be 5-9, meaning each infected person can be expected to infect 5-9 other people. “When you think about diseases that have an R0 of 8 or 9 – there aren’t that many.”
  • Asked about the contents of the slide deck, Walensky said, “There weren’t any surprises. It was the synthesis of the data all in one place that was sobering.”

What comes next:

  • The CDC is scheduled to publish additional data Friday that will back Walensky's controversial decision to change guidance for fully vaccinated people. She said Tuesday the CDC was recommending that even fully vaccinated people wear masks indoors in places where transmission of the virus is sustained or high.

CNN's Paul LeBlanc and Maggie Fox contributed reporting to this post. 

9:24 a.m. ET, July 30, 2021

Covid-19 cluster in Massachusetts town shows vaccines are "clearly working," official says

From CNN's Adrienne Vogt

The data behind an internal US Centers for Disease Control and Prevention document that suggests fully vaccinated people might spread the Delta variant at the same rate as unvaccinated people is, according to the Washington Post, based on a Covid-19 cluster that emerged from July 4 weekend festivities in Provincetown, Massachusetts.

Alex Morse, Provincetown’s town manager, told CNN's "New Day" that there are 112 active cases right now in the town, but the overall cluster number is more than 880 since July 1.

Morse said 74% of the overall cases were among fully vaccinated individuals — but he credits vaccines with ultimately saving people’s lives. 

“What's been interesting, and I think the silver lining here, is that the vaccine is clearly working. It is meant to prevent hospitalization and certainly prevent death. There hasn't been a single death related to the cluster here in Provincetown. There hasn't been a spike in hospitalizations,” Morse said. 

According to the internal CDC, which was first reported by The Washington Post, the Delta variant is about as transmissible as chickenpox, with each infected person on average infecting eight or nine others.

Provincetown reinstated its indoor mask mandate after the cluster of Covid-19 cases emerged.

“The Delta variant is incredibly dangerous to unvaccinated individuals. And While we have a mask mandate in the short term, our longer term way out of this is really through vaccination,” Morse said. 


8:43 a.m. ET, July 30, 2021

Vaccination by itself is not enough to stop the spread of Covid-19 variants, study finds

From CNN’s Maggie Fox

Vaccination alone won't stop the rise of new variants and in fact could push the evolution of strains that evade their protection, researchers warned Friday. 

They said people need to wear masks and take other steps to prevent spread until almost everyone in a population has been vaccinated.

Their findings, published in Nature Scientific Reports, support an unpopular decision by the US Centers for Disease Control and Prevention to advise even fully vaccinated people to start wearing masks again in areas of sustained or high transmission.

"When most people are vaccinated, the vaccine-resistant strain has an advantage over the original strain," Simon Rella of the Institute of Science and Technology Austria, who worked on the study, told reporters.

"This means the vaccine resistant strain spreads through the population faster at a time when most people are vaccinated."

But if so-called non-pharmaceutical interventions are maintained – such as mask use and social distancing – the virus is less likely to spread and change. "There is a chance to remove the vaccine resistant mutations from the population," Rella said.

The findings suggest that policymakers should resist the temptation to lift restrictions to celebrate or reward vaccination efforts.

This is likely to be especially true with a more transmissible variant such as the Delta variant, said Fyodor Kondrashov, also of the Institute of Science and Technology Austria.

"Generally, the more people are infected, the more the chances for vaccine resistance to emerge. So the more Delta is infectious, the more reason for concern," Kondrashov told reporters. "By having a situation where you vaccinate everybody, a vaccine resistant mutant actually gains a selective advantage."

People should not complain, he said. "The individual who already vaccinated and putting on a mask should not think this is pointless but should think that there is a vaccine resistant strain running around," he said.

8:20 a.m. ET, July 30, 2021

CDC will release data supporting its mask guidance today

From CNN's John Bonifield and Maggie Fox

The US Centers for Disease Control and Prevention said it will release a study Friday that supports this week’s decision to change mask guidance.

CDC Director Dr. Rochelle Walensky said Tuesday the agency was changing guidelines for fully vaccinated people because of new science.

She said even fully vaccinated people should wear masks indoors in areas where transmission of the virus is substantial or high.

Walensky said new data indicated that people who get breakthrough infections involving the Delta variant of the virus can be as likely to infect someone else as unvaccinated people are. And she promised that data would be released soon.