The state public health order issued on Aug. 5 applies to indoor visits, and requires those who aren't vaccinated to have tested negative for COVID-19 within 72 prior to the visit.
Visitors who are vaccinated can show their physical vaccination card, a photo of the card, documentation from a health care worker or a digital QR code.
As of last week, just over 76% of eligible people in California had received at least one dose of a vaccine. However, public health officials say the state continues to see increasing numbers of people, overwhelmingly unvaccinated, being admitted to the hospital and ICU with COVID-19.
The order goes into effect as the state is also requiring that California's roughly 2.2 million health care workers and long term care workers be fully vaccinated by Sept. 30.
The order is different than what Gov. Gavin Newsom said last month when he announced health care workers would have the choice of either getting vaccinated or submitting to weekly testing.
Now, the order does not give health care workers a choice. It says all must be fully vaccinated by the end of September, with exceptions for people who decline the vaccine because of a religious belief or workers who cannot be inoculated because of a qualifying medical reason backed up by a note signed by a licensed medical professional.
"Health care facilities are high-risk settings where COVID-19 outbreaks can have severe consequences for vulnerable populations including hospitalization, severe illness, and death. By requiring health care workers to be fully vaccinated and visitors to acute care facilities to demonstrate they are fully vaccinated or have tested negative for COVID-19, California is protecting the most vulnerable individuals, while also protecting workers in these settings," the state Department of Public Health said in a press release.
The Associated Press contributed to this report.