As soon as kids get out of school it goes away for a while. When children are in school they are passing it around. Once they start in the fall it starts to creep up, peaks in Jan. (when the majority are catching it), starts to go down in the Spring (when most of the kids have already been exposed) and then when they are out for summer and not passing it around it goes down. Of course there are camps and such to continue the spread but it's not NEARLY as bad or concerning. There aren't nearly the amount of large groups of children in the summer as there are during the school year, so that's the reasoning for the drop in the warm months.