By Lynne Adkins

PHILADELPHIA (CBS) — Flu season is getting a quick start, and a miss in the vaccine may be to blame.

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When working on the influenza vaccine for the following year, researchers make a guess as to which strains will be prevalent. This year, one strain mutated after the vaccine was already in production, so the vaccine isn’t a perfect match.

According to Dr. Michael Jhung, medical officer at the Centers for Disease Control, it’s that mutated strain that’s making people sick.

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“The H3N2 component of the vaccine is different from the H3N2 virus that’s circulating,” he explains. “When that happens, it may be that the vaccine won’t work as well.”

Dr. Jhung says it’s rare for the vaccine not to match the flu strains — it’s only happened twice in the past 20 years.

So, should you still get a flu shot? He says yes — there will still be some protection.

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