The flu season finally is ending after a record-breaking struggle with two unexpected strains.
Its culmination brings hope that next season's vaccine will be more effective than this year's version that largely missed the mark.
The Allegheny County Health Department is ending its formal surveillance and reporting program for the 2007-08 flu season, which featured almost double the confirmed cases and almost triple the number of suspected cases of the previous record season.
This season ended with 639 influenza cases confirmed through positive lab cultures, far surpassing the county record of 395 lab-confirmed cases in 2004-05. Another 1,573 suspected cases were identified through positive rapid antigen tests given in doctors' offices. That easily broke the previous county record of 545 suspected cases in 2004-05.
Health Department spokesman David Zazac said the vaccine was only 44 percent effective this season because two influenza strains showed up that it did not cover.
The vaccine covered Type A Solomon Islands, Type A Wisconsin and Type B Malaysia flu strains. While it was effective against Type A Solomon Islands early in the season, it was less effective against Type A Brisbane that showed up in February, then Type B Yamagata that showed up in March and April.
"Eighty percent of the time, the vaccine matches up well [with actual flu virus strains]," Mr. Zazac said.
"This year was the other 20 percent, when it didn't match up."
Dr. Andrew Sahud, chairman of the Infection Prevention and Control Committee at Allegheny General Hospital, said people also showed more resistance this year to the commonly prescribed flu medications Tamiflu and its generic, Oseltamivir phosphate.
"The estimate this year is that there's been about a 6 [percent] to 8 percent resistance to Tamiflu and Oseltamivir, so that's a problem," Dr. Sahud said.
"They can reduce the severity, but if we're stuck with a less effective vaccine and a medicine with emerging resistance, treatment options are more limited."
Because many people never see a doctor or get tested for influenza, the numbers of confirmed and suspected cases represent only a small fraction of actual flu cases countywide, the Health Department noted.
In the typical flu season, about 600 county residents die from complications related to the flu, Mr. Zazac said. The Centers for Disease Control and Prevention said in a typical year 5 percent to 20 percent of the nation's population gets the flu, leading to 200,000 hospitalizations from complications and 36,000 deaths.
Based on CDC definitions, the flu was at epidemic levels throughout the season. Even though the vaccine was less effective than it had been in previous years, it did help reduce symptoms and prevent hospitalizations.
"Some cases we did see were more severe than previous years," Dr. Sahud said. "Unfortunately, in cases where we asked people if they got the flu vaccine, most people in the hospital said 'no.' "
David Templeton can be reached at email@example.com or 412-263-1578.