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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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.