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Flu Season Was Milder Than Usual

But certain strains of germs showed resistance to antiviral drugs, report notes

THURSDAY, June 15, 2006 (HealthDay News) -- The 2005-06 flu season was a mild one in the United States, peaking in early March and producing no unusual number of deaths, federal health officials reported Thursday.

"The bottom line is it was only a mild-to-moderate flu season," said Dr. Marc Siegel, clinical associate professor of medicine at New York University School of Medicine. "It appeared in all states but did not come close to reaching epidemic status."

"It was a mild season," added Lynette Brammer, an epidemiologist with the influenza branch of the U.S. Centers for Disease Control and Prevention.

Brammer co-authored a report on the flu season that appears in the June 16 issue of the CDC's Morbidity and Mortality Weekly Report.

Flu reached its peak during the week ending March 11 when 25 states reported widespread activity and 16 states reported regional (confined to a given region) activity. All told, 38 states and New York City reported widespread flu activity at least once during the 2005-06 season. All states reported at least regional activity at some point during the season.

The flu season was not without its dramas, however.

Researchers found an extremely high level of resistance among circulating viruses to the antiviral medications amantadine and rimantadine.

"There was a dramatic resistance, going practically overnight from 12 percent to more than 90 percent," said Siegel, author of Bird Flu: Everything You Need to Know About the Next Pandemic.

As a result, CDC officials recommended in January that doctors stop using this adamantane class of antivirals for the treatment and prevention of flu. Despite the directive, a high level of resistance continued to be observed through May.

The percentage of deaths due to pneumonia and influenza did not reach epidemic proportions, peaking at 7.8 percent once during the week of Jan. 14 and again during the week of March 16. This was lower than deaths reported during the five preceding flu seasons, which ranged from 8.1 to 10.4 percent.

"The peak percentage never exceeded the threshold for an epidemic," Brammer confirmed. "This is a reflection of a fairly mild season. The fact that it was a long season could have impacted that as well. If your deaths are spread over a longer period of time, you don't get those sharp peaks. But even saying that, it looks mild."

From October 2, 2005, through June 3, 2006, a total of 35 children under the age of 18 died from causes related to influenza. The deaths were reported in 13 states -- Arizona, California, Colorado, Connecticut, Kansas, New Jersey, New Mexico, Oklahoma, Pennsylvania, Rhode Island, Vermont, Virginia, and Wyoming, as well as New York City.

This year's vaccine was a fairly good match for the particular viruses that circulated, Brammer said.

For next year's season, the U.S. Food and Drug Administration's Vaccines and Related Biological Products Advisory Committee has recommended changes to the influenza A (H3N2) strain, along with the B strain.

"Typically, we change one or two of three strains each year because the viruses are constantly changing," Brammer said.

"There are influenza strains that have been emerging that have not been covered in prior vaccines," Seigel explained.

On the avian flu front, the report stated that between Dec. 1, 2003, and June 13, 2006, a total of 225 people worldwide have been infected with avian flu, and 128 have died.

"The year was also marked by a continuing progression of H5N1 (avian flu) in birds and in the occasional human but with no sign that it is about to transform into the next pandemic," Siegel said.

More information

The U.S. Centers for Disease Control and Prevention has more on the flu.

SOURCES: Lynnette Brammer, MPH, epidemiologist, influenza branch, U.S. Centers for Disease Control and Prevention, Atlanta; Marc Siegel, M.D., author, clinical associate professor of medicine, New York University School of Medicine, New York City, and author, Bird Flu: Everything You Need to Know About the Next Pandemic; June 16, 2006, Morbidity and Mortality Weekly Report
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