LOS ANGELES — All attendees at California indoor events with more than 1,000 people in attendance will have to show proof of COVID-19 vaccination or a negative COVID test within 72 hours of the event, according to rules announced Wednesday by the state Department of Public Health.

The state previously allowed people to simply "self-attest" to being vaccinated or having tested negative, but the new rules — which take effect Sept. 20 — require attendees to show proof. The previous guidelines also applied only to events with 5,000 or more people, but the new rules lower the threshold to 1,000.

"The delta variant has proven to be highly transmissible, making it easier to spread in large crowds where people are near each other for long periods of time," said Dr. Tomas Aragon, the state public health officer. "By requiring individuals to be vaccinated, or test negative for COVID-19 at large events, we are decreasing the risk of infection, hospitalization and death."

The announcement is the latest in a series of vaccination or testing mandates imposed in a variety of sectors. The state already requires all school workers to show proof of vaccination or submit to weekly testing. All workers at health-care facilities in the state must be vaccinated by Sept. 30.

Various cities are also imposing vaccination requirements for workers. The Los Angeles City Council voted Wednesday to impose such a mandate on its workers, and the city of Santa Ana announced a similar requirement.

Los Angeles County this week will impose a mask-wearing mandate for all attendees at outdoor "mega-events" with 10,000 or more people. The county already requires masks at all indoor public settings, including large-scale events such as concerts and basketball games.

Leaders of two major entertainment companies threw their support behind the state's vaccine-or-testing mandate for indoor events, issuing statements through the state. 

"Today's announcement adds another layer of protection to make our state, our venues and our communities safer," said Dan Beckerman, president/CEO of AEG. "Our fans, our team members and our families all want to feel as protected as possible from COVID-19 while enjoying our favorite concerts and sporting events. We are proud to partner with public health officials to continue to play a role in encouraging those who haven't gotten vaccinated to follow the advice of the medical experts."

Michael Rapino, president/CEO of Live Nation Entertainment, added, "Vaccination and health check requirements ensure everyone can continue enjoying live music while also encouraging even more people to go get vaccinated, which is why Live Nation has made this the standard at our venues and festivals across the country. We fully support California's efforts and will stay in lockstep to keep bringing live music back to the Golden State."