With coronavirus cases up by nearly 50 percent since Thanksgiving, California announced Monday a statewide indoor mask requirement will go into effect on Wednesday.

Under the order, which is set to expire on Jan. 15, masks must be worn while in indoor public spaces. Some counties, including Los Angeles and Ventura, implemented indoor mask mandates during the summer, and the new order will cover counties that do not have a mandate in place, the Los Angeles Times reports.

California imposed its first statewide mask mandate in 2020, which was lifted in June. The Centers for Disease Control and Prevention says California is seeing a high level of transmission of the coronavirus, and state health officials believe this could indicate the start of a winter surge. The highly contagious Delta variant is still the dominant strain in the United States, and public health experts are working to determine how the newly discovered Omicron variant operates.

Masks make a difference in stopping the spread of the virus, Dr. Mark Ghaly, California’s health and human services secretary, told reporters on Monday, and “even a 10 percent increase in indoor masking can reduce case transmission significantly. Wearing a mask is going to be one of the most important things to help us get through this period of uncertainty. This is a critical time where we have a tool that we know has worked and can work.” Californians, he added, “have done this before. And we of course believe we can do it again.”