Health officials generally guide providers to expect 36,000 deaths annually from influenza. But a federal report shows that the numbers of flu deaths vary widely year-to-year. In the 1986-87 flu season there were just 3,349 deaths. In 2003-04 there were to 48,614.
"Flu deaths are a moving target," said David Shay, MD, medical officer with the Centers for Disease Control and Prevention's influenza division, in a media briefing. Year to year, he said, flu forecasters can only guess what the year will look like based on the pathogenicity of circulating strains.
Shay said the CDC is shifting thinking about influenza deaths as a flat 36,000 annual number. "The CDC is trying to move away from a single number, and rather, give a range over a particular period of time to give a better time text to what flu really means in terms of what it does to the community ."
H3N2 strains cause much more severe disease than other strains. For example, "the average mortality rates for the 22 seasons during which influenza A(H3N2) was a prominent strain were 2.7 times higher than for the nine seasons that it was not," the CDC report said.
During A(H3N2) prominent seasons, the number of deaths was 36,631 compared with 13,544 in seasons when non-A(H3N2) strains were prominent. Why that occurred is unclear.