This month marks the two-year anniversary of the arrival of the Covid-19 vaccine in Marin County, one of the most vaccinated counties in the nation. But Marin also has higher numbers of elderly residents than surrounding areas, and as the so-called tripledemic of respiratory illness sweeps the region, Marin’s hospitals are functioning at near capacity. The number of respiratory syncytial virus, or R.S.V., cases seems to have peaked locally, while Covid and influenza cases continue…