The latter group was found to have a higher Th2 polarization in the immune response with a greater production of IL-4 and lower levels of IFNγ; therefore, they hypothesize the presence of two phenotypes of bronchiolitis: the first with RSV infection during the peak period and the second with a possible genetic predisposition to atopy and hospitalized during the non-peak season (29). The gene discussed is IL4; the disease is bronchiolitis.