Sure looks to me like it was something that happened in October.
Disease spread is exponential. Perhaps there is an ongoing set of infections that formed the baseline number around Sept. 1, and then schools acted as a partially-separate subpopulation in which spread started slowly before gaining steam in October.
This hypothesis is inspired by Hawaii data, as Hawaii has a clear flu season even though the weather is similar all year long. One explanation in Hawaii would have to do with schools; another would be that tourists from colder climates are artificially generating a flu season when they visit Hawaii. Edit: on second thought, assuming “week 0” corresponds to Jan 1 in that data, I think it fits the tourist hypothesis better. Also, it’s fair to say that there may be months in Hawaii when people systematically stay indoors, facilitating spread of flu. But that would include school.
Disease spread is exponential. Perhaps there is an ongoing set of infections that formed the baseline number around Sept. 1, and then schools acted as a partially-separate subpopulation in which spread started slowly before gaining steam in October.
This hypothesis is inspired by Hawaii data, as Hawaii has a clear flu season even though the weather is similar all year long. One explanation in Hawaii would have to do with schools; another would be that tourists from colder climates are artificially generating a flu season when they visit Hawaii. Edit: on second thought, assuming “week 0” corresponds to Jan 1 in that data, I think it fits the tourist hypothesis better. Also, it’s fair to say that there may be months in Hawaii when people systematically stay indoors, facilitating spread of flu. But that would include school.