Just 1,345,064 travelers were screened at U.S. airports on Tuesday, the lowest since May 18 when 1,408,017 were screened, the TSA said.

United CEO Scott Kirby said Monday he thinks holiday travel will return to normal.

-ABC News' Sam Sweeney

San Diego has become the first county in the U.S. to declare that health misinformation is causing a public health crisis in its community. This follows the County Board of Supervisors' 3-2 vote Tuesday night.

Changes to county strategy to combat the pandemic will include: labeling health misinformation and providing timely health information to counter it; modernizing public health communications; investigating in digital resources and training for health practitioners and health workers; and developing a website to be a central resource for fighting health misinformation.

The new policy was introduced when 96.7% of hospitalizations in San Diego County were residents who were not fully vaccinated.

KISS co-lead singer Gene Simmons tested positive for COVID-19, the band shared on its Twitter page Tuesday evening.

In a statement, the band said the 72-year-old was experiencing "mild symptoms."

His diagnoses comes less than a week after co-lead singer Paul Stanley, 69, tested positive for COVID-19 as well.

In a statement released on Aug. 26, the band said that, "everyone on the entire tour, both band and crew, are fully vaccinated."

KISS has postponed four of its "End of the Road" tour shows from Sept. 1 to Sept. 5.

"The band and crew will remain at home and isolate for the next 10 days," the band said in a statement.

Peter Marks, the director of the Food and Drug Administration's Center for Biologics Evaluation and Research (CBER), announced the upcoming departure of two top vaccine regulators to his staff in an internal memo, which was obtained by ABC News.

Dr. Marion Gruber, director of the FDA's Office of Vaccines Research and Review (OVRR) and her deputy, Dr. Phil Krause, are set to leave the agency in October and November respectively, according to the memo.

Krause, who's been with the agency for over a decade, and Gruber, who has been with the FDA for over 30 years, were instrumental in the review and authorization of the three COVID-19 vaccines, the memo said.

The memo said that Gruber will be "retiring" and gave no other details about Krause's departure.

ABC News has reached out to both Gruber and Krause for comment.

When reached for comment about their departure, an FDA spokesperson told ABC News the agency is "confident in the expertise and ability of our staff to continue our critical public health work, including evaluating COVID-19 vaccines."

Their departures come at a critical time for the vaccine review team. After facing pressure to move as fast as possible to get vaccines' full licensure done, the agency is now weighing booster shots for a wider pool of Americans.

The timing of the booster shot approval has been a bone of contention amongst federal agencies after the Biden administration announced the availability of booster shots would begin ahead of any ruling from the FDA or Centers for Disease Control and Prevention advisory groups.

-ABC News' Sasha Pezenik

A new study by the U.S. Centers for Disease Control and Prevention estimates that roughly 83% of blood donors in the nation have either been vaccinated against COVID-19 or were previously infected with the virus.

This, however, does not mean that more than 80% of Americans are immune from infection. That's because neither vaccination nor prior infection provides 100% protection -- antibodies are just one part of the overall immune response, and immunity wanes over time. The analysis also may overestimate the portion of people with antibodies because blood donors may be more likely to be vaccinated or have previously been infected.

The study, posted online Tuesday by JAMA Network Open, a monthly open access medical journal published by the American Medical Association, took a snapshot of the presence of antibodies from COVID-19 vaccination or prior infection in about 1.4 million donated blood samples from across the United States. The repeated cross-sectional analysis was conducted each month during July 2020 through May 2021, before delta became the predominant variant of the novel coronavirus in the U.S.

The study shows that the number of blood donors who tested positive for antibodies, indicating either vaccination or prior infection, has gone up over time, from 3.5% in July 2020 to 20.2% for infection-induced antibodies and 83.3% for both infection- and vaccine-induced antibodies in May 2021.

Being vaccinated offers better protection compared to prior infection, and it's recommended that people who have previously contracted COVID-19 should still get inoculated.

-ABC News' Katie Bosland and Sony Salzman