• More than 90% of U.S. counties are now experiencing high or substantial rates of Covid transmission, CDC Director Dr. Rochelle Walensky said Thursday.
• "As we have been saying, by far, those at highest risk remain people who have not yet been vaccinated," she said.
• The average number of daily Covid vaccinations tripled in Arkansas and quadrupled in Louisiana, Alabama and Mississippi over the past month.

The delta Covid variant has spread so rapidly across the U.S. that most counties in the country now meet the CDC's guidelines recommending people wear masks indoors — whether they are vaccinated or not.

"We continue to see cases, hospitalizations and deaths increase across the country. And now, over 90% of counties in the United States are experiencing substantial or high transmission," Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, told reporters at a briefing Thursday. "As we have been saying, by far, those at highest risk remain people who have not yet been vaccinated."

The CDC updated its mask guidance on July 27 to recommend masks indoors in areas of the U.S. where community transmission was considered high or substantial. Most counties that were experiencing high transmission rates were in Southern states, but in two weeks the spread of the highly transmissible delta variant expanded to most counties across the country.

The CDC recorded 132,384 new cases of Covid on Wednesday, reaching a seven-day average of about 113,000 cases per day, jumping almost 24% from the prior week, she said. Hospital admissions have similarly climbed by about 31% over the previous week to about 9,700 per day.

Unvaccinated Americans make up the overwhelming majority of hospitalizations and deaths across the country, she said.

Several large institutions in both the public and private sector have mandated vaccines or require weekly Covid testing to prevent further spread of the virus. President Joe Biden recently met with private-sector leaders to encourage vaccine or testing mandates.

"Vaccination requirements are gaining momentum across the country and are already covering tens of millions of workers, educators, college and university students and health-care providers," White House Coronavirus Response Coordinator Jeffrey Zients said at the briefing. "They will help keep communities safe and stop the spread of the virus."

Several cities with high vaccination rates have also mandated vaccination for indoor activities at such places as restaurants, bars and gyms to prevent further spread of the delta variant. New York City will require at least one dose of a vaccine for indoor activities, and San Francisco will require full vaccination with a two-dose regimen or one dose of a single-dose regimen vaccine. Zients said some 700 colleges and universities have instituted vaccine mandates across the country.

In the hardest-hit states, vaccination rates are climbing as residents take precautions against the spread of the delta variant, he said. The average number of daily shots tripled in Arkansas and quadrupled in Louisiana, Alabama and Mississippi over the past month, Zients said.

The CDC also reinforced its vaccine guidance for pregnant people on Wednesday, reiterating that the vaccine is safe for those who are pregnant or plan to become pregnant. Walensky cited new data that "did not find any safety concerns for pregnant people who are vaccinated late in pregnancy, or for their babies," she said.

"Ending this pandemic requires every American to do their part. So, please, if you're unvaccinated, get your shot ... it's never been more important," Zients said.