By Luis Fábregas

Published: Friday, January 11, 2013, 2:46 p.m.
Updated: Wednesday, January 23, 2013

Got a flu shot and feeling pretty confident you'll be spared from this year's nasty flu season?

Don't be so sure.

A nationwide study conducted partly in Pittsburgh estimated on Friday that this season's vaccine is 62 percent effective, which means you still might end up in the doctor's office.

“The flu vaccine is far from perfect, but it's still by far the best tool we have to prevent the flu,” said Dr. Tom Frieden, director of the Centers for Disease Control and Prevention. “Childhood vaccines get 90 percent efficacy, and that's what we'd like to see.”

In explaining the vaccine's power, Frieden said people who receive it are 62 percent less likely to require a doctor's check-up or hospitalization than those who don't. In the past, flu vaccine effectiveness has ranged between 50 percent and 70 percent, he said.

Changes in the influenza strains circulating from year to year make it difficult for scientists to deliver a better vaccine, said Dr. Richard Zimmerman, professor of family medicine at the University of Pittsburgh School of Medicine. The vaccine typically contains a mix of flu viruses.

“It's hard to come up with a more effective vaccine because the flu changes all the time,” Zimmerman said. “The challenge is that you have to keep making a new vaccine each year.”

UPMC and the University of Pittsburgh's Schools of the Health Sciences operate one of five national sites that studied the vaccine's effectiveness as part of the U.S. Flu Vaccine Effectiveness Network. There were 251 local participants with acute respiratory illnesses, the most participants from all the sites, which collected specimens and analyzed data from 1,155 people nationwide.

Zimmerman said 83 of the local participants had the A strain of the flu virus that causes more severe symptoms.

“It's been a fairly severe season in this region at this point,” he said. While B strains of the virus have not been as prevalent in this region, Zimmerman said that may change as the season progresses.

This season's flu shot, which authorities estimate has been given to about 130 million people, contains vaccines for both strains.

The CDC's Frieden said the flu is likely to continue for several weeks. The typical flu season can last about three months.

“The only thing predictable about flu is that it's unpredictable,” Frieden said. “Only time will tell us how long the season will last and how moderate or how severe this season will be in the end.”

In its weekly analysis of flu activity, the CDC reported the virus was widespread in 47 states, up from 41 the prior week. The disease has killed 20 children 17 and younger. While flu activity might have peaked in some parts of the country, it typically ebbs and flows during the winter.

Some local hospitals have been jammed with patients complaining of flu-like symptoms. Dr. Joseph Bresee, a medical epidemiologist with the CDC, said other viruses might be to blame, including a norovirus that causes vomiting and diarrhea.

Luis Fabregas is a staff writer for Trib Total Media. He can be reached at 412-320-7998 or lfabregas@tribweb.com.

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