I see you've already accepted @JakeKaupp's nice answer, but I thought I would throw in a different option, using geom_dotplot. The data you are visualizing is rather small, so why not forego the boxplot?
ggplot(box, aes(x = factor(year), y = case, fill = code))+
geom_dotplot(binaxis = 'y', stackdir = 'center',
position = position_dodge())
