After nasal immunization with a vaccine containing influenza virus hemagglutinin (HA) and mucosal adjuvant, the main antibody detected in nasal washes is
Correct answer: B. IgM against hemagglutinin
The main antibody detected in nasal washes after immunization with a vaccine containing influenza virus hemagglutinin (HA) and mucosal adjuvant is IgM, as it is the primary type of antibody involved in local immune responses at mucosal surfaces.