Covid is surging in Marin, which now has the highest case rates in the Bay Area. In the past 10 days, the county’s case rates have more than doubled, but its high vaccination rate means the surge isn’t accompanied by rising hospitalizations. Just one person was hospitalized with the virus in Marin this week, illustrating the effectiveness of vaccines at preventing severe disease. Dr. Matt Willis, the county’s public health officer, told the Board of Supervisors on Tuesday that in response, Marin will begin monitoring hospitalizations, rather than case rates, as its metric for re-enacting policies like indoor mask mandates. “The relationship between cases and severe illness has been uncoupled because of high vaccination rates,” Dr. Willis said. A lab study released Wednesday by Pfizer and BioNTech indicated two doses of their vaccine may be insufficient to protect against the Omicron variant, which has not yet surfaced in Marin, but a booster offered strong protection. Dr. Willis said the county is routinely analyzing about 25 percent of positive tests for the variant, paying special attention to tests from international travelers.