Comparative Immunogenicity and Cross-Clade Protective Efficacy of Mammalian Cell-Grown Inactivated and Live Attenuated H5N1 Reassortant Vaccines in Ferrets

Abstract

Continued H5N1 virus infection in humans highlights the need for vaccine strategies that provide cross-clade protection against this rapidly evolving virus. We report a comparative evaluation in ferrets of the immunogenicity and cross-protective efficacy of isogenic mammalian cell-grown, live attenuated influenza vaccine (LAIV) and adjuvanted, whole-virus, inactivated influenza vaccine (IIV), produced from a clade 1 H5N1 6:2 reassortant vaccine candidate (caVN1203-Len17rg) based on the cold-adapted A/Leningrad/134/17/57 (H2N2) master donor virus. Two doses of LAIV or IIV provided complete protection against lethal homologous H5N1 virus challenge and a reduction in virus shedding and disease severity after heterologous clade 2.2.1 H5N1 virus challenge and increased virus-specific serum and nasal wash antibody levels. Although both vaccines demonstrated cross-protective efficacy, LAIV induced higher levels of nasal wash IgA and reduction of heterologous virus shedding, compared with IIV. Thus, enhanced respiratory tract antibody responses elicited by LAIV were associated with improved cross-clade protection.

Impact of Prior Seasonal H3N2 Influenza Vaccination or Infection on Protection and Transmission of Emerging Variants of Influenza A(H3N2)v Virus in Ferrets

“…The differences in IgA and IgG antibodies between the immunization groups were not evident using the standard HI assay. These results are consistent with the ability of a live attenuated influenza vaccine to elicit higher levels of nasal wash IgA and greater reduction of virus shedding than an inactivated influenza virus vaccine (20,25). Although the precise immunological mechanism(s) involved in viral clearance was not addressed in the current study, it is reasonable to speculate that raised antibody levels in the ferret respiratory tract of virus-infected ferrets would have a greater capacity to neutralize virus infectivity and blunt transmission.…”

“…Ferret IgG and IgA antibodies were detected using a modified ELISA procedure as previously described (20,25). Flat-bottom 96-well microtiter plates (Immulon II; Dynatech Laboratories, Chantilly, VA) were coated with 100 HAU per well of purified Perth/09 inactivated virus overnight at 4°C.…”

Characterization of Reverse Genetics-Derived Cold-Adapted Master Donor Virus A/Leningrad/134/17/57 (H2N2) and Reassortants with H5N1 Surface Genes in a Mouse Model

“…In summary, these data and previous studies (53) indicate that pandemic 6:2 reassortant vaccine virus based on caLen17 MDV generated through the established reverse genetics system provides candidate vaccine viruses with preclinical safety and immunogenicity profiles consistent with successful development of human vaccines for H5N1.…”

“…Vaccinated mice remained healthy and showed no evidence of weight loss. Cross-clade protective immunity induced by caVN-Len17rg vaccine virus was previously evaluated in a ferret model (53) and compared to inactivated vaccines. Both vaccines were highly immunogenic and protective against homologous challenge following double immunization.…”

Complexities in Ferret Influenza Virus Pathogenesis and Transmission Models

“…While young adult ferrets (generally 4 to 12 months old) are most frequently used, the age of animals employed can vary depending on the questions addressed in the study, ranging from ferrets that are newly weaned (Յ8 weeks old) to aged ferrets (Ͼ4 years of age) (11,12). The choice of anesthetic used for inoculation and sampling postinoculation (typically ketamine cocktails of various compositions and dosages administered intramuscularly, inhaled isoflurane, or both) can vary between laboratories, leading to differences in the depth of sedation and the respiration rates of sedated animals (13)(14)(15)(16).…”