Live attenuated influenza vaccine is safe and immunogenic in immunocompromised ferrets

Patients undergoing chemotherapy for cancer are highly susceptible to influenza virus infection. Prevention of influenza virus infection is complicated in the immunocompromised host because of suboptimal responses to the trivalent inactivated influenza vaccine (TIV). A new, live attenuated influenza vaccine (LAIV; FluMist) may offer a more effective alternative to TIV, but the safety of this LAIV in immunocompromised patients must first be established. In the present study, FluMist was administered to ferrets immunocompromised by treatment with dexamethasone and cytarabine. Ferrets exhibited no signs or symptoms attributable to FluMist, and nasal clearance of LAIV strains from immunocompromised ferrets was similar to that from control ferrets. Serum antibody responses against the vaccinating strains were analyzed as a measure of vaccine efficacy. Antibody titers to all 3 vaccine strains in immunocompromised ferrets were similar to those seen in mock-treated control ferrets, as assessed by microneutralization assay. These findings support the potential use of this vaccine in immunocompromised humans.