The nasty trifecta of respiratory illnesses known as the tripledemic is losing some of its punch in Marin County, although Covid rates remain stubbornly high. The number of flu cases began falling in mid-December, and the decline has continued since then, said Lael Duncan, deputy public health officer for Marin County. The latest county data also indicates a continuing decline in cases of respiratory syncytial virus, or R.S.V. “The good news is, the number of people presenting with influenza has sharply decreased, and it appears we’ve passed our peak with R.S.V.,” Dr. Duncan said. Public health officials routinely analyze wastewater samples to measure the extent of the viruses throughout the county. Though the latest tests show a decrease in R.S.V. and flu, they indicate that the Covid-19 virus has not begun to decline. The latest reporting shows 11 people hospitalized for Covid-19 in Marin, with three undergoing treatment in intensive care units. “We don’t see a plateau in Covid cases yet,” Dr. Duncan said. Health officials strongly encourage people to get vaccinated for flu and Covid. The latest Covid vaccine, known as the bivalent booster, has proven effective against the latest variants of the virus. Treatments are available for both flu and Covid, and are especially important for older people, those with underlying medical conditions and anyone with a compromised immune system.