The county reported 506 new cases, more than double the amount of cases that were reported June 15, when the state and county lifted most COVID-19 restrictions.
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The county's rate of people testing positive for the virus held steady at 1.2% on Thursday, but that's triple the rate the county was reporting on June 12, and a jump from the 0.8% rate reported just last Friday.
County Public Health Director Dr. Barbara Ferrer said the increase in COVID-19 illness and death is happening much more in communities of color where vaccination rates are rising the slowest.
Those ages 18 to 49 remain a concern, but Ferrer is seeing progress among the youngest residents.
RELATED: LA County health officials recommend wearing masks indoors amid spread of Delta variant
LA County recommends masking indoors amid spread of Delta variant
Ferrer said the county is tracking the number of fully vaccinated people who test positive and the numbers show the vaccines remain highly effective. She said even at extremely low infection rates, there have still been more than 2,000 people who were fully vaccinated but contracted the virus out of more than 4 million.
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She said that while small, the chance that fully vaccinated people could potentially be infected with the Delta variant or any form of COVID-19 contributed to the county's call this week for everyone - regardless of vaccination status - to wear masks in indoor public settings.
It wasn't known how many of those breakthrough cases documented in the county involved the Delta variant. Ferrer noted that last week, when the county had identified 123 Delta variant cases, only 10 of them involved fully vaccinated people.
Delta variant of COVID-19 a rising concern in Los Angeles County
Delta variant of COVID-19 a rising concern in Los Angeles County
She said there is still much to learn about the more contagious Delta variant, which studies show may cause even more serious disease and death.
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Ferrer said the latest sampling reveals the Delta variant is showing up in more cases, and that vaccinations would stop its transmission.
In hopes of encouraging more people to get vaccinated, the county is continuing to offer incentives. Beginning Friday and continuing until next Thursday, anyone who gets vaccinated at sites operated by the county, city of Los Angeles or St. John's Well Child and Family Center will be entered for a chance to win one of four ticket packages for the Huntington Library, Descanso Gardens, Los Angeles County Arboretum and South Coast Botanic Garden.
The packages include an annual membership to the Huntington and one-day passes to the other facilities.
City News Service contributed to this report.