As a widespread flu outbreak rages throughout Louisiana, health officials on Thursday said the vaccine might be less effective due to a mutation of the virus.

The “widespread” designation doesn’t typically happen until January or February, said Dr. Marilyn Reynaud, regional administrator medical director with the Louisiana Department of Health and Hospitals.

“It’s unpredictable when it starts every year, but we are definitely seeing an uptick in influenza reports,” Reynaud said.

Louisiana and Alaska were the only states with “widespread” outbreaks of influenza for the week ending Nov. 22, according to the most recent weekly surveillance report by The Centers for Disease Control and Prevention.

Recent pharmaceutical data also reflect the outbreak in Louisiana.

New Orleans ranked No. 3 and Baton Rouge ranked No. 6 among metro areas hit hardest by flu cases the week of Thanksgiving, according to a weekly flu index launched by Walgreen Co. The index is based on the number of antiviral prescriptions filled at Walgreens stores.

But an early start to flu season doesn’t provide researchers clues to the potential impact of the virus, said Dr. Raoult Ratard, the Louisiana state epidemiologist.

“There’s no connection to when it starts and the severity,” he said.

While the flu can keep youngsters home from school, it has not yet hurt attendance rates, said Keith Bromery, spokesman for the East Baton Rouge Parish School System.

“Flu season always has an impact, but we’ve not seen any dip in attendance so far,” he said.

Influenza causes a variety of symptoms, including fever, chills, coughing, weakness and body aches, according to the DHH website.

The illness kills more than 400 Louisiana residents every year, the department estimates.

While reports of the virus are flowing in across the state, it’s not clear why the outbreak has hit Louisiana particularly hard, said Dr. Frank Welch, medical director for the DHH immunization program.

“The only thing that’s predictable about the flu is that it’s unpredictable,” he said.

Influenza’s fickleness stems from its tendency to mutate, Welch said. And it appears the virus has done just that, according to a report by the CDC.

The agency on Wednesday issued a warning that the current flu vaccine might not be a perfect match for the strain currently spreading throughout the U.S., due to a mutation from the virus last year.

Influenza A (H3N2) is the most common strain of the virus reported so far this season. This strain has previously been tied to higher rates of hospitalization and death, Welch said.

The vaccine, however, can still help protect from the virus, Welch said.

“Even with the mutation, it’s still the same virus,” he said. “So the vaccine might work just as well. We don’t know yet.”

Along with vaccinations, Welch advocates what he calls the “kindergarten rules.”

“Wash your hands, cover your coughs and stay home when you’re not feeling well,” he said. “It’s not worth getting other people sick.”

Follow Matt McKinney on Twitter, @Mmckinne17.