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Flu Season Hitting Its Peak

After slow start, widespread activity reported, U.S. officials say

THURSDAY, March 3, 2005 (HealthDay News) -- Flu activity has increased steadily in the United States since late December and, as of mid-February, may not have peaked, federal health officials report.

But after a slow start, 2004-2005 is shaping up as a fairly typical flu season, according to the U.S. Centers for Disease Control and Prevention.

"This [the prospect of a late February peak] is not something unexpected or out of the ordinary," said Lynnette Brammer, an epidemiologist in the CDC's influenza branch. "Influenza often peaks in February. Last year was unusual because it peaked early in the season. This year is more typical."

The uptick in flu activity "basically is happening all over" the country, Brammer said. "The Pacific coast area may have a little less activity than other places, but basically activity has increased everywhere."

Worries that a new strain of flu virus not covered by existing vaccines -- and the headline-grabbing lack of available vaccines -- might cause a major outbreak are unfounded so far, Brammer said. The 11,587 positive sputum samples detected this season by the National Respiratory and Enteric Virus Surveillance System were "the usual suspects," she said -- about 85 percent Type A and 15 percent Type B flu.

The findings are contained in the March 4 issue of the CDC's Morbidity and Mortality Weekly Report (MMWR).

Statistics gathered since the last report don't indicate when the flu season will start to slack off, she said: "We just have to wait and see. We hope we're getting close to the peak of activity, but we just don't know."

In the context of year-to-year activity, this season is not unusual, the MMWR statistics show. The weekly percentage of sputum specimens that tested positive for flu has been no higher than 26.7 percent. Over the last three seasons, peaks ranged from 24.9 percent to 34.7 percent positive.

For the week ending Feb. 19, a total 33 states reported widespread influenza activity; 15 states reported regional activity; and two cities -- New York City and the District of Columbia -- reported local activity. Since early October, 38 states and New York City have reported widespread flu activity for at least one week, the report said.

During the week ending Feb. 19, a total of 8.5 percent of deaths reported from 122 cities were attributed to flu and pneumonia, slightly above the epidemic threshold of 8.2 percent. The percentage of deaths exceeded the epidemic threshold during three non-consecutive weeks from Oct. 3 to Feb. 19, but otherwise has stayed below the threshold, according to the CDC.

In October 2004, pediatric deaths due to flu became a "nationally notifiable condition," according to the report. As of Feb. 19, nine pediatric deaths had been reported nationwide. During the 2003-2004 season, 153 pediatric deaths were due to the flu, the CDC said.

Worries about this flu season escalated in October when health regulators in Great Britain suspended the manufacturing license of the Chiron Corp.'s Liverpool plant, citing bacterial contamination. The plant was expected to supply about half the estimated 105 million doses for the United States. About 21 million doses of vaccine from other sources were distributed after the shortage was reported.

"With all the attention paid to influenza vaccine early in the year, people kept expecting an outbreak to occur," Brammer said. "This late peak may have surprised people a little."

Concerned consumers got a dose of good news Wednesday when British officials gave Chiron permission to resume vaccine production at the Liverpool plant. But the company still needs approval by the U.S. Food and Drug Administration before it can start selling vaccines here.

Dr. Jesse L. Goodman, director of FDA's Center for Biologics Evaluation and Research, said the agency will examine the Liverpool plant before making a decision.

"When all critical stages of manufacturing are in full swing, and needed corrective actions can be fully evaluated, FDA plans to conduct a comprehensive inspection of Chiron's Liverpool facility to assure that Chiron can produce a safe and effective vaccine," Goodman said in a statement.

The FDA probably will inspect the plant early in the spring, an agency spokesperson said.

Vaccine for next winter's flu season already is being produced at the Swiftwater, Penn., plant of Sanofi Pasteur, the largest supplier, which has a capacity to make 50 million to 60 million doses a year.

Other companies, such as GlaxoSmithKline, which sells a flu vaccine overseas, and ID Biomedical of Canada, may also enter the U.S. market, The New York Times reported Thursday.

More information

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

SOURCES: Lynnette Brammer, MPH, epidemiologist, U.S. Centers for Disease Control and Prevention, Atlanta; March 4, 2005, Morbidity and Mortality Weekly Report
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