Supposedly there are 4 strains of flu in the wild this season and the shot is only effective against two. Every year it has to be predicted which strains will be common, in order for the shots to be mass produced in time to distribute them. Most years the prediction is accurate, but sometimes it's wrong or incomplete. My sister had the shot earlier this season, and she got the flu last week. She couldn't move much and had to stay in bed for most of the week, so it was a real doozy. Glad you're feeling well enough to release some blades!