Want to attend a large indoor event in California? You’ll now have to prove that you are vaccinated from COVID-19 or you have recently received a negative coronavirus test.

That’s according to a new statewide mandate that kicked in this week. It was the first such requirement of its kind in the nation when California announced the measure back on Aug. 18.

The move was unveiled as public health officials encouraged more people to get vaccinated while they simultaneously sought to combat a surge in cases spurred by the highly contagious delta variant.

“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,” Dr. Tomás J. Aragón, California’s public health officer, said at the time. “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.”

Since then, the number of reported coronavirus cases have trended downward in California and the state’s coronavirus case rate is now the lowest in the U.S.

Here’s what to know as the new measure takes effect:

What it affects

The rule applies to all indoor “mega events,” which is defined by the state as a crowd of at least 1,000 people at an inside venue, according to the California Department of Public Health’s guidelines.

These gatherings include sports games, concerts, conventions, expos and conferences.

Typically, these events “may be either general admission or gated, ticketed, and permitted events,” and could have either assigned or unassigned seating, the state says.

What is required

Attendees of indoor “mega events” must now provide proof that they are fully vaccinated against COVID-19 or tested negative for the coronavirus within 72 hours of the event starting, according to state public health officials.

Acceptable forms of vaccination proof include the person’s vaccine card — even a photo of it — or a QR code.

Those who can’t get the vaccine yet, including children under the age of 12, are covered by the testing requirement.

As part of the revised restrictions, self-attestation is no longer an accepted form of verifying one’s vaccine status or negative test result.

The updated measure is set to expire on Nov. 1.

What is exempt

Venues such as shopping malls or museums are not generally covered under the new rule because they “are open to public circulation as part of their regular operations,” according to the state’s website.

The only exception is if such places host a large indoor gathering that would qualify as a mega event.

A similar proof of vaccination or negative test result has been “strongly recommended” — but not mandated — at outdoor gatherings where more than 10,000 people are in attendance. Examples include sporting events, concerts, parades, marathons, car shows, and food or music festivals.

However, Los Angeles County is set to require attendees show either proof of COVID-19 vaccination or a recent negative coronavirus test at all outdoor mega events beginning next month.

The rule will also apply to those who visit the county’s two major theme parks, Universal Studios Hollywood and Six Flags Magic Mountain.