Flu, RSV trending upward and COVID remains flat as holiday season arrives

Coronavirus cases have been flat locally, likely due to the outsized surge that occurred this past summer, but the flu appears to be ramping up on its traditional trajectory, indicating that the latest spike of cases will be seen in late December and early January.

The latest weekly respiratory virus report from the county health department recorded 322 flu cases last week, up from 232 two weeks ago but still only about half of the 420 cases observed during the same week last year. COVID-19 cases show a flatter trend with 168 reported last week, 219 two weeks ago and the previous year’s weekly total at 897.

Test positivity rate, the percentage of all ordered tests that come back positive, shows the split with about 5% of flu tests confirming an infection. The number was about 2% for coronavirus.

Dr. Erik Berg, interim medical director of the county’s epidemiology and immunization services branch, said on Wednesday afternoon that while it is an educated guess that COVID rates are lower because of the summer surge, it is difficult to make definitive statements about the behavior of a virus that has been in the world for such a relatively short time.

“Certainly prior immunity from vaccinations or prior infection is playing a role, but how much is unclear,” Berg said. “I would not be surprised if we still get a big spike this winter as we have in previous winters, but it’s hard to tell with such a new virus where we only have a limited number of years in which it has been circulating.”

We have much, much more experience observing flu seasons, Berg said, and there is no reason to expect that the 2024-25 winter months should be much different than usual.

“The southern hemisphere did have a fairly busy influenza seasons, and the vaccine effectiveness in South America was about 35% in terms of preventing hospitalization,” he said.

“It’s a little bit different each year, but I do think we’re prepared for a busy flu season.”

Locally, the vaccination pace is roughly similar to last year with the county’s vaccine registry recording 761,891 total flu vaccinations administered through Nov. 16. Though the bulk of the 1 million or so vaccines received most years have already been administered, Berg noted that, with immunity building to full strength in about two weeks, it’s still possible to have protection in place for Christmas.

2024 The San Diego Union-Tribune. Distributed by Tribune Content Agency, LLC.