The study, based on data from the 43,127 cases in Los Angeles County from May 1 through July 25, was published by the CDC's Morbidity and Mortality Weekly report. The study also found that those who are unvaccinated are almost five times more likely to contract COVID-19 than those who are fully vaccinated.
During this period, LA County's percentage of fully vaccinated adults jumped from 27% to 51%.
"These data remind us that if you are not yet vaccinated, you are among those highest at risk," CDC Director Rochelle Walensky said in a White House briefing Tuesday.
On Monday, the Food and Drug Administration granted full approval to the Pfizer-BioNTech COVID-19 vaccine.
The Biden administration is hopeful that the authorization will encourage those who were skeptical about the safety of the vaccine to finally get the shot.
As of Tuesday, about 61% of Americans have received at least one dose of a vaccine; 52% are fully vaccinated as cases, deaths and hospitalizations continue to rise back to the levels of the earlier months of the pandemic due to the delta variant.
Walensky, in the briefing, reminded Americans that it is still possible to contract COVID-19 even if you are fully vaccinated, but it is "far less common than unvaccinated people getting COVID-19. And most importantly, their conditions are far less severe."
The CDC does not require its employees to be vaccinated.
"The federal government does not mandate (require) vaccination for individuals," the CDC website reads. "For some healthcare workers or essential employees, a state or local government or employer, for example, may require or mandate that workers be vaccinated as a matter of state or other law."