There's a new flu shot every year, to match the particular flu strains floating around. Some years the shot isn't a good match. Even so, the flu shot is still a good bet.

Self-esteem and self-confidence seem like pretty much the same thing, but they're not. For example, maybe you can easily get in front of a crowd, give a speech, and command a room, which shows self-confidence, but at the same time, you feel like crap about your own public speaking, which is a lack of self-esteem.