To avoid getting sick including flu, Japanese people do ugai (a gargle) and tearai (washing hands) often especially coming back home from outside. Japanese kids are taught these by parents and teachers.
Because there are tons of bacteria outside, people get sick because of bringing and having them. In Japan actually doing ugai and tearai are the simplest and cheapest ways to protect us from bacteria.
If you come visit Japan in fall or winter, you would see so many posters and booklets which tell you how important ugai and tearai are!