"This is the most severe flu season we've seen in Wisconsin since 2008, when the H3N2 strain was also common," Belongia said. "The CDC recommends that anyone who has not already been vaccinated should get the vaccine."Although it takes about two weeks to be fully protected, the flu season began early and likely will continue for weeks. Getting vaccinated now can provide additional protection if the season continues through February and into March. It's particularly important for young children, pregnant women, the elderly and people with chronic health conditions to get vaccinated, because they have the highest risk of serious illness, hospitalization or death from the flu. For the report, researchers looked at data from 1,155 children and adults who had acute respiratory infections between Dec. 3 and Jan. 2. In Marshfield, testing began in mid-December, and more than 500 patients have been enrolled. About 50 percent of those tested were positive for one of the flu viruses. There have been multiple reports of flu cases in people who were vaccinated this year. According to Belongia, it's not uncommon to see flu cases in vaccinated people, and physicians should not base their treatment decisions on whether a person has been vaccinated. The CDC recommends initiating antiviral treatment as soon as possible for people who are seriously ill with influenza or at high risk for complications. "While the flu vaccine is the best intervention we have at this time, there is a need for more research to develop a new generation of influenza vaccines with even higher and longer-lasting protection," Belongia said. The Marshfield Clinic Research Foundation was the first site to receive CDC funding to study influenza vaccine effectiveness, and was the sole provider of this information for four flu seasons beginning in 2004-2005.