After a slight increase in virus transmission likely due to spring break travel, county regulations did not loosen this week as expected. Despite the fact that Marin boasts high vaccination rates, its population remains vulnerable to Covid-19, public health officials underscored. Compared to 42 percent of Californians and 7 percent of people globally with one dose, 76 percent of Marin residents over age 16 are partially vaccinated. Still, given that it can take up to six weeks for the full effect, only around a third of Marin’s adult residents likely have immunity through vaccination. “What can still go wrong? We are obviously making progress in the pandemic in most parts of the United States, and in California, cases do continue to decline and most counties are in the orange tier, but there is still plenty of room for outbreaks,” Dr. Matt Willis, the county’s public health officer, said Tuesday. “We can have mask fatigue and the breakdown of nonpharmacological intervention—we’ve seen some of that in Marin in the past two weeks.” Marin was anticipated to become the first Bay Area county to drop into the least restrictive tier in the state’s economic reopening system, assigned the color yellow. That tier—which would allow businesses to increase capacity, bars to open indoors and outdoor gatherings to have up to 100 people—requires less than two cases per 100,000 residents over two weeks. Marin’s case numbers were just below that threshold until last week, when they exceeded it; last Tuesday, 15 people tested positive. Now, the soonest Marin could move into the yellow tier is May 4. Should vaccination rates remain high and hospitalizations low statewide, Gov. Gavin Newsom has set June 15 as a juncture to dissolve the tier system and reopen the economy. The county is marking a milestone in its pandemic response: For the first time, the vaccination rate of minorities has exceeded that of whites. Overall, 94 percent of people over age 65 have received at least one dose; in that age group, 96 percent of Latinos have received a shot, compared to 78 percent of whites. For residents age 45 to 64, Blacks have the highest vaccination rate at 71 percent, compared to 60 percent of Latinos, 56 percent of Asians and 48 percent of whites. Among the youngest residents, Latinos have the highest rate. Yet Mr. Willis cautioned that the county’s demographic numbers are based on 2010 census data, so the vaccine rates could be inflated. Despite Marin’s successful distribution, herd immunity remains elusive, Dr. Willis said. His goal is to have around 90 percent of the population vaccinated. Around 20 percent of Marin’s population is under age 16 and ineligible for a vaccine; should Pfizer receive clearance to vaccinate youth ages 12 to 15, another 8 percent of the population would become eligible. Looking ahead, Dr. Willis sees many uncertainties in how the pandemic may unfold. “There’s a question around waning immunity: How long will the protection of the vaccine last? That’s an unanswered question. We hope that the vaccine will provide lifelong protection, but it’s unlikely that will be the case,” he said. This week, Marin’s health department received $8,585,474 in federal assistance to continue battling the pandemic, including to fund testing, case investigation and contact tracing, surveillance, containment and mitigation—and to generally help better prepare the county to respond to the virus over the next 24 months. On the coast, attention remains focused on vaccinations. Madeline Hope, director of the Tomales Bay Youth Center, received $60,000 from a state initiative to address vaccine hesitancy through an education campaign. “The goal is to reach the hard-to-reach individuals and the most vulnerable people,” she said. “Whether you are getting vaccinated or choosing not to get vaccinated, we want contact with you and want to understand what your reasons are. We need an integrated response and understanding of how to get through this together.”