The period of early exposure was at least 4 years of continuous exposure (the subjects were at least 11 months old, the 3-days a week feeding was until they were 60 months old). The nature of seasonal allergies tends to be that while early natural exposure is common, early and continuous natural exposure is not.

So I wouldn't view natural environmental exposure to seasonal allergens as a valid basisi on which to reject the idea that the kind of early and continuous exposure at issue here might work for seasonal allergens.