THURSDAY, April 16, 2009 (HealthDay News) -- Confirming earlier reports, U.S. health officials said Thursday that the 2008-09 flu season was one of the milder seasons in recent years.
Less severe strains of influenza and a good vaccine match for the strains that were circulating combined to create a milder season this year than last, according to the U.S. Centers for Disease Control and Prevention.
The percentage of deaths attributable to pneumonia and flu, and the percentage of outpatient visits "suggest that this season has been less severe than the 2007-08 season and is more similar to the 2005-06 and 2006-07 seasons," CDC officials wrote in the April 17 issue of the agency's Morbidity and Mortality Weekly Report.
Flu activity was low from late September through early January, before peaking in mid-February, and remaining high until the middle of March. Since then, infections rates have been falling nationwide, according to the CDC.
"If we look at mortality and the rate of hospitalizations, it seems like this year is less severe compared to last year and more similar to the years prior to last year," Dr. Alicia M. Fry, a CDC epidemiologist, told HealthDay earlier this month. "The flu did not reach an epidemic threshold this year."
Historically, she explained, in years where the influenza type A H3N2 subtype is the predominate virus, the season is more severe. "This year was not one of those years," she said. "It was a year where the influenza A H1N1 virus was the predominate virus, followed by the influenza type B viruses."
The CDC based its conclusions on data from 122 cities on deaths from flu or pneumonia among adults and flu-related deaths among children. It appears that flu-related hospitalizations and deaths were significantly lower this year, Fry said.
Typically, the flu causes 200,000 hospitalizations and 36,000 deaths a year, according CDC estimates. The old, the very young and people with chronic illnesses are at greatest risk.
So far this flu season, 45 children have died from the flu or related complications, compared with 68 during last year's flu season, according to the CDC.
Flu vaccines are often 70 percent to 90 percent effective. Last flu season, the vaccine was only about 20 percent effective against the H3N2 strain and less than 2 percent effective against the B strains, according to the CDC.
But this year's flu vaccine was a very good match for influenza A H1N1 and H3N2, Fry said.
That was fortunate, because there had been concerns about antiviral resistance, she said. The drug Tamiflu (oseltamivir), routinely prescribed to people with the flu, was resistant to this year's H1N1 strain, and the H3N2 flu strain was resistant to two other antivirals -- rimantadine (Flumadine) and amantadine (Symmetrel).
The U.S. Centers for Disease Control and Prevention has more on the flu.