Flu Cases Spreading At Very High Levels Across CA, Strain Capable Of Reinfections On The Rise

If it's seems like everyone is getting sick, that's ikely because cases of influenza are surging across California somewhat late in the flu season.

So far this flu season, more than 154,000 people have tested positive for influenza, a vast undercount wastewater data shows. Nearly 19,000 cases were confirmed in the first week of Februray. According to the California Department of Public Health, every county in the state is seeing the flu spread at 'very high' or 'high' levels, with the highest rates of spread currently across all of Southern california and the very northern counties of the state.

"Many regions in California are experiencing very high levels of seasonal influenza activity," state health officials warned in a written statement. "Test positivity, emergency department visits, and hospitalizations from influenza are all increasing statewide."

Influenza cases rose slowly starting in November, before exploding in mid-December, according to data from the California Department of Public Health. By early January, cases peaked, followed by a small dip in positive case rates that health officials hoped meant flu season would end early this year.

But cases again rose to an eaven higher peak in February, the data reveals.

Seasonal flu activity remains elevated across the country, including in California, where children are among the most impacted, according to state health officials.

"Children and kids are always the first to register new trends," Dr. Caitlin Rivers, an epidemiologist who writes about infectious disease, told CNN. "So I do think that the increase will hit adults as well, but for now, it’s really concentrated in kids."

So far, more than 14,600 people have been hospitalized in California due to the flu, and 262 have died, including three children, according to data from the Department of Public Health.

Flu activity this year has been mostly driven by a new mutation called "subclade K." Subclade K is an Influenza A strain H3NS that has mutated seven times, making the flu a more serious threat than in years past.

The subclade K mutation emerged after the vaccine was chosen for the Northern Hemisphere, last February. Once the mutation became established, there wasn’t time to develop a better-matched vaccine. That leaves more people susceptible because the virus has found a way to evade pre-existing immunity from either an infection or vaccination.

It seems, however, that Influenza B strains may be on the come-up, according to CNN. Influenza B differs in that a person can get it more than once in a season. In California during the week ending Feb. 7, cases of Influenza B appeared to nearly double, reaching 15,300 confirmed cases. However, Influenza A remains dominent in the golden State, with more than 17,100 cases confirmed last week.

Health officials recommend people protect themselves and their families from sickness by getting updated COVID-19 and flu vaccines, and RSV vaccines for people over 60 years old. Officials also advise people to take additional precautions, such as avoiding people who are sick, washing hands and wearing a mask.

"Current seasonal flu vaccines remain effective at reducing severe illness and hospitalization, including the currently circulating viruses," Dr. Erica Pan, CDPH Director and State Public Health Officer, said in a January statement. "As a pediatrician, parent, and daughter, I have made sure that my own family is protected with this season’s flu vaccine."

Local Editor Kristina Houck and AP News contributed to this report.