Like Christmas and lefse, influenza has returned for another winter.

The Minnesota Department of Health announced the state's first lab-confirmed flu infection on Thursday -- a 26-year-old woman from Olmsted County -- and encouraged people to schedule flu shots. The strain that was tested is targeted by this year's vaccine, a department official said.

"The first case ... serves as a reminder that vaccination is the best way to protect yourself and others against influenza, and [that] the best time to get vaccinated is now," said Kristen Ehresmann, who directs the department's immunization programs.

The infected woman, who had not been vaccinated, suffered no unexpected complications and did not require hospitalization.

Although the flu season typically runs from October to April, the first lab-confirmed case usually isn't discovered until mid-November. The early discovery doesn't indicate that this year's flu season will be unusually severe, Ehresmann said, but it does mean that widespread transmission of the virus can be expected in eight to 10 weeks.

"It does start the clock," she said.

Last year's flu season followed a predictable pattern, with the virus emerging in November, becoming widespread by late January 2011, and tapering off in March. (Widespread means the virus has been discovered in half the state's flu reporting regions.) It contrasted with the historic 2009-'10 flu season, in which a new H1N1 strain circulated in the spring of 2009 and then surged in the fall, until a vaccine was created to counteract it.

Ehresmann said the flu strains used to create this year's vaccine are the same as those used in last year's vaccine. However, she stressed that people vaccinated last year still need shots this year because the seasonal vaccine wears off.

Flu symptoms include sore throat, cough, fever, headache, muscle aches and fatigue. It can turn severe, especially in the elderly and those with underlying health conditions, and Health Department officials urged anyone with severe symptoms to see a doctor. Influenza is caused by a virus and antibiotics are not effective against it.

Jeremy Olson • 612-673-7744