According to NHK, many people in Japan caught influenza even though they had flu shots. Flu virus may be mutated in season 2011-2012.
According to the statistics from the local health research centers from Kobe City, Yokohama City, Mie Pref, Saga Pref and Sakai City, more than 80% of flu virus samples were mutated type A (H3N2) (especially 100% in Kobe). Those mutated flu virus were not effective by this year's vaccine.
The flu shots are not perfect. Each year, the drug companies forecast the trend of the flu in the previous summer because they cannot manufacture the vaccine quickly.
According to NHK, the drug companies might not be able to predict the mutated flu virus completely.
Therefore, there have been more chances to catch flu this year. People needs to be cautioned.
NHK added that the people, who had a vaccine shot, did have fewer chances to catch flu. So it was not completely worthless to have a flu shot.
Although the season is coming to the end, even if you have a flu shot in Japan, you should still be careful with flu.
Wash your hands, gargle your throat when you came from crowded place and/or outside. Drink a lot of water and eat heathly diet!