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…