Why this could be a nasty flu season in California

Why this could be a nasty flu season in California

After two perilous winters of surging COVID-19, it’s the last news you want to hear — this year’s flu season is hitting early, and it could be the worst in many years. 

Flu hospitalizations are ramping up this year earlier than they have in a decade, according to the latest federal health data. That aligns with predictors, including data from the Southern Hemisphere, which often serve as a preview for the Northern Hemisphere’s flu season. 

“We saw a severe influenza season in Australia during our summer of 2022 (their winter) so this was a herald that our influenza season may get worse,” Dr. Monica Gandhi, a professor of medicine and an infectious diseases doctor at UCSF, wrote in an email.  

One of the biggest drivers of flu activity is likely so-called “immunity debt,” according to Gandhi. Fewer people than usual have been exposed to the flu over the last two years, thanks to school closures and masking. But this winter is different, with people leaving their masks at home and gathering indoors more freely, leading to wider spread. That means immune systems aren’t as well-primed to clear the virus as they are in a typical year, leading to more infections that cause serious illness, or at least stick around long enough to be detected.

About 7.9% of California flu tests came back positive on Oct. 23, compared to a 0.3% positivity rate at the same time last year, according to state data. The overall incidence rate is relatively low in the Bay Area and higher in the southern part of the state, said Stanford infectious diseases expert Dr. Abraar Karan, but “this could change quickly.” 

There are also some indications that fewer people are getting flu shots this year, further depressing population immunity. Public health officials are recommending that everyone six months and older get the flu shot as soon as possible. All three experts who spoke with SFGATE said that it’s perfectly safe to get flu and COVID vaccines simultaneously.

Medical experts warn of a severe flu season ahead this winter. 

About 7.9% of California flu tests came back positive on Oct. 23, compared to a 0.3% positivity rate at the same time last year, according to state data.

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How well the vaccine works for each individual “depends on which flu type you get infected with,” according to UCSF infectious diseases expert Dr. Peter Chin-Hong. Flu vaccines are produced months in advance, based on infections during the Southern Hemisphere’s flu season.

While it remains unknown how effective this year’s flu vaccine will be against the strains that end up circulating most widely here, the predominant strain in the U.S. right now is H3N2, one of four strains included in this season’s shot. High rates of H3N2 infection have historically driven more severe flu seasons, “particularly for older adults and young children,” the CDC said in a press release.

Despite signs of a relatively quiet COVID winter, experts are worried about the potential of a bad flu season combining with the residual effects of the pandemic to further strain America’s already-stressed health care system.

“350 people are still dying per day in the US from COVID – and that number is likely going to increase as COVID cases increase in the community,” Chin-Hong said.

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