influenza
"My wife woke up Monday morning feeling off and by 3pm felt terrible and running a 102 degree fever.  Immediately took her to urgent care and she tested positive for H3N2 (the strain that wasn't in the vaccine).  She took her first dose of Tamiflu around 8pm.  By the next day she was feeling a lot better and by Wednesday morning, the fever was gone and she felt 95% better.  Then on Thursday, my 4 year old woke up with a fever of 101.  By the time we got in to see his Dr (2pm) his temp was 103 and he was feeling TERRIBLE (and he also tested positive).  He got his first dose around 5pm and woke up the next morning with a temp of 98.6 and he felt GREAT!  Completely amazed.  No side effects for either of them."