https://www.siliconvalley.com/2021/12/28/contra-costa-county-covid-mask-rules-omicron/

Contra Costa County will again require everyone — vaccinated or not — to wear masks indoors at all times as COVID-19 cases and hospitalization rates begin to soar.

Only a month ago, amid a decline of COVID cases, the county eased up on its mask rules by allowing fully vaccinated groups of 100 or fewer people to remove their masks in “controlled spaces” such as workplaces and gyms.