Cross-clade immunity in cats vaccinated with a canarypox-vectored avian influenza vaccine

Several felid species have been shown to be susceptible to infection with highly pathogenic avian influenza (HPAI) viruses of the H5N1 subtype. Infection of felids by H5N1 HPAI virus is often fatal, and cat-to-cat transmission has been documented. Domestic cats may then be involved in the transmission of infection to other animals but also to humans. A particular concern is the hypothetical role of the cat in the adaptation of the virus to mammalian species, thus increasing the pandemic risk. Therefore, the development of a HPAI vaccine for domestic cats should be considered a veterinary and also a public health priority. Here we show that vaccination of cats with a recombinant canarypox (ALVAC^®1) virus, expressing the hemagglutinin (HA) of influenza virus A/chicken/Indonesia/03 (H5N1) confers protection against challenge infection with two antigenically distinct H5N1 virus isolates from humans. Despite low hemagglutination inhibiting (HI) antibody titers at the time of challenge, all vaccinated cats were protected against mortality and had reduced histopathological changes in the lungs. Importantly, viral shedding was reduced in vaccinated cats as compared to controls, suggesting that vaccination of cats could reduce the risk of viral transmission. In conclusion this study showed that the recombinant canarypox virus protected cats against homologous and heterologous H5N1 HPAI virus challenges.