Influenza activity decreased statewide to "local" levels last week with no new influenza deaths reported as of Feb. 23, according to the South Dakota Department of Health.
Of the 33 influenza-associated deaths in the state this season, two have been children: one infant and one 12-year-old boy with an underlying chronic illness. Fifty-two percent of victims were female.
The remaining deaths were among people 75 years of age and older, except for one person in their 50s, according to state epidemiologist Lon Kightlinger.
"The reason why the flu vaccination is less effective in the elderly is because as we age our immune system weakens, which causes our response to vaccinations to deteriorate," Kightlinger said Friday.
The peak of the 2012-13 flu season came in early January, state health officials said. So far this year, three-fourths of the laboratory-confirmed viruses were Influenza A.