A typical day at Dr. Daniel Levy's pediatrics practice in Owings Mills provides a snapshot of the current flu epidemic, as five to 10 youngsters show up with the telltale fever, aches, cough and other miseries that mark the seasonal disease.
"This year has been a bear," said Levy, who might see almost as many flu patients in a single day now as he saw during the entire 2006-2007 season.
Across the country, doctors are reporting far heavier flu caseloads than they did in the previous two years, which saw a decline in the cyclical illness. One reason: This year's flu vaccine turned out to be a less-than-perfect match for the strains of virus that are actually infecting people.
Fashioning each season's flu vaccine is a medical roll of the dice. Manufacturers package it with killed or weakened versions of three viral strains that showed up at the close of the previous season in the Far East.
Because the virus drifts eastward, flu experts predict that those strains will be active in North America in the next season.
Usually, the predictions are accurate - but not always. "By the time they form the vaccine and the virus reaches our shores, the strains of flu can mutate," Levy said.
Vaccine mismatches have occurred in only three of the past 19 years, said Curtis Allen, a spokesman for the U.S. Centers for Disease Control and Prevention.
This winter, many flu victims are falling ill with a Type A virus that scientists have dubbed "Brisbane" after the Australian city where it previously appeared. It is a genetic variant of the so-called Wisconsin strain that's included in this season's vaccine.
So the vaccine provides only partial protection against Brisbane, possibly reducing its duration or severity but not preventing it altogether. As it turned out, a second vaccine strain was a complete mismatch - but, according to the CDC, it's Brisbane that's driving the epidemic.
Rene Najera, an epidemiologist with the Maryland Department of Health and Mental Hygiene, said the flu season is shaping up to be the worst since 2004-2005. So far, doctors have reported 2,400 cases to the health department, including 397 people who needed to be hospitalized.
So far, 147 of those admitted were children and 250 adults. No deaths have been reported.
About 226 patients have been admitted to the Johns Hopkins Hospital this year - evenly split between children and adults. Typically, people most vulnerable to flu's complications are young children, the elderly and patients with chronic illnesses that weaken their immune systems.
