LOS ANGELES (CBSLA.com/AP) — The Centers for Disease Control now says this year’s flu vaccine is the least effective in a decade.

The agency said Thursday that the vaccine is only 23 percent effective.

“The influence of viruses is always changing and keeping up with them means we have to constantly update the influenza vaccine. Effectiveness can range from 10 to 60 percent,” Dr. Alicia Fry of the CDC said.

The poor showing is primarily because the vaccine doesn’t include the bug that is making most people sick.

Each year, the flu vaccine is reformulated, based on experts’ best guess at which three or four strains will be the biggest problem. Those decisions are usually made in February, months before the flu season, to give companies that make flu shots and nasal spray vaccine enough time to make enough doses.

More than 25 states are reporting a very active flu season already.

Local cases of the flu have risen over the past several weeks and officials expect the numbers to get worse as the peak of the flu season has yet to hit, the Los Angeles County Health Department said.

Despite the low effectiveness of the vaccine, the CDC still recommends that people get the flu shot.

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