A spike in RSV and COVID-19 cases led health officials in Northern California to encourage residents to wear masks in public. The advisory was released on Wednesday, December 27, by Yolo County Public Health and is based on data collected by researchers from the lab at the University of California, Davis.

“I recommend that everybody in the community take steps to protect themselves from infection, including wearing a high-quality mask when indoors around others,” said Yolo County’s Public Health Officer Dr. Aimee Sisson in a statement.

The lab at UC Davis has been at the forefront of tracking COVID-19 since the start of the pandemic in 2020 by testing the city’s wastewater treatment plant for traces of the virus. The lab leads the Healthy Central Valley Together project. This program allows professors in the university’s Civil and Environmental Engineering Department to test samples from eight partner facilities four times a week. The partner facilities are located in Yolo, Merced, and Stanislaus counties, giving the lab a comprehensive look at COVID-19 infection rates in the area. Lab professionals extract the RNA and genetic material from the virus, enabling them to measure the concentration. 

Their most recent data indicates high levels of COVID-19 and respiratory syncytial virus, or RSV. Per the data, cases of COVID-19 and hospitalizations due to the virus have been on the rise in the area. The latest variant of COVID-19, dubbed JN.1, is the cause of the increase in infections. JN.1 currently accounts for 44% of all COVID-19 cases nationwide after first being identified in September. It is reportedly more infectious but less severe than other strains. Those who have already caught mild cases of JN.1 report being miserable for three to four days with typical COVID-19 symptoms like a cough, fever, body aches, and fatigue.

Yolo County was identified by the US Center for Disease Control and Prevention as one of several Northern California counties with the highest COVID-19 hospitalization rates last week. Data found that between Yolo, Sacramento, El Dorado, and Placer, the region currently has 246 hospital admissions related to COVID-19. Those at high risk include older adults, infants, people with compromised immune systems, those with chronic health issues, and those who are pregnant.

Placer County’s interim health officer, Dr. Rob Oldham, told CBS13 that this uptick in COVID-19 cases is expected. Many respiratory viruses like COVID and the flu see spikes with the arrival of colder weather. Viruses spread easily and quickly with increased travel and family gatherings around the holidays. Dr. Oldham gave similar advice to Dr. Sission, recommending wearing high-quality masks, self-testing, and staying up to date on vaccines. While JN.1 is too new to have been thoroughly tested, there is no evidence to suggest that vaccines and masks will not work against the new variant. The latest COVID-19 vaccine provides decent cross-protection across all active variants.