Flu and RSV are sustaining California’s sniffly season, COVID yet to surge this winter

The season of sniffles and coughs has come again. But while influenza and RSV activity is “moderate and increasing” around California, COVID activity is unusually low for the holiday season.

The most recent weekly update from the California’s Department of Public Health shows the test positivity rate for flu has risen by nearly 4 percentage points in a week to 13.2%​ as of Dec. 14, the most recent available data. The COVID positivity rate is at 2.3%, rising 0.2 percentage points from the previous week.

The health department’s weekly updates are posted most Fridays, but the respiratory virus reports for the last two weeks of the year are not reported until January.

“COVID is rising, but influenza is leading the pack right now,” said Dr. John Swartzberg, clinical professor emeritus at the UC Berkeley School of Public Health.

Since COVID emerged at the end of the 2019-2020 respiratory virus season, it has been by far the most deadly of the respiratory viruses for which the state tracks and publishes weekly data, though it has killed fewer people each of the last few years compared to early in the pandemic.

Since July 1, there have been 1,873 COVID deaths across California — with the summer surge not subsiding until late August — and 89 flu deaths.

After the late summer surge, COVID deaths once again reached new lows, and testing, hospitalizations and deaths are just now starting to show signs of an increase as we head into the new year.

“If you look at wastewater data, COVID is clearly rising throughout the United States and certainly in California,” Swartzberg said.

In Santa Clara County, wastewater measurements show the same pattern. County public health officials monitor local wastewater and test for concentrations of the viruses in four local sewersheds. According to aggregated wastewater surveillance data monitored by the state health department, COVID levels in the entire Bay Area region have just crossed from low to medium and are increasing.

Influenza concentrations started to rise in November and have continued to rise through December. RSV, or respiratory syncytial virus, has been on the rise since late November. Swartzberg said that RSV may have peaked, but COVID is still expected to surge later in the season.

COVID has been at low concentrations in the county’s four sewersheds since the middle of October after a prolonged surge that lasted from June through August, with concentrations measuring at high concentrations for much of that time around the county.

Now COVID levels seem to be the lowest they’ve been in December in the past several years. “It’s looking better than last year, and last year was the best winter we had,” Swartzberg said.

Even though COVID vaccination numbers are lower than they were in the first years of their availability, some immunity from this summer’s surge is still lingering in the community. But the number of people who have received the most recent vaccination is “disappointingly low,” in Swartzberg’s opinion. Influenza vaccination rates are higher but nowhere near early COVID vaccination rates.

A new RSV vaccine, which is recommended for the very young, those over 75 and some other high-risk people, might be contributing to the overall improvement in rates of that virus this year compared to last year, Swartzberg said. Since the beginning of this respiratory virus season on July 1, California has reported 21 deaths due to the virus, including four children, compared to 33 at the same point last year. “RSV looks like it’s on track for a better year,” he said.

And while a lot has changed, including the prevalence of COVID at this year’s holiday dinner tables compared to the last few years, Swartzberg’s general advice has not: “Please get immunized. It’s not too late.”