Serum antibody response to influenza viruses after one and two doses of intranasal vaccine.

Groups of three ferrets were vaccinated intranasally with the indicated 1st dose of vaccine and 42 days later were inoculated with a 2nd dose of vaccine (H5N1 HK03 ca or VN04 ca). Serum samples were collected 6 weeks after the 1st dose (pre-dose 2), 1 week and 3 weeks after the 2nd dose, respectively, and antibody titers (geometric mean titers from 3 animals) against the first or second vaccine viruses were determined by microneutralization assay.