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

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