Whereas, multiple vaccine types have been developed to curb the spread of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) among humans, there are very few vaccines being developed for animals including pets. To combat the threat of human-to-animal, animal-to-animal, and animal-to-human transmission and the generation of new virus variants, we developed a subunit SARS-CoV-2 vaccine which is based on the recombinant spike protein extracellular domain expressed in insect cells and then formulated with appropriate adjuvants. Sixteen 8–12-week-old outbred female and male kittens (n = 4 per group) were randomly assigned into four treatment groups: spike protein alone; spike plus ESSAI oil-in-water (O/W) 1849102 adjuvant; spike plus aluminum hydroxide adjuvant; and a PBS control. All animals were vaccinated intramuscularly twice, 2 weeks apart, with 5 μg of spike protein in a volume of 0.5 ml. On days 0 and 28, serum samples were collected to evaluate anti-spike IgG, antibody inhibition of spike binding to angiotensin-converting enzyme 2 (ACE-2), neutralizing antibodies against wild-type and delta variant viruses, and hematology studies. At day 28, all groups were challenged with SARS-CoV-2 wild-type virus 106 TCID50 intranasally. On day 31, tissue samples (lung, heart, and nasal turbinates) were collected for viral RNA detection, and virus titration. After two immunizations, both vaccines induced high titers of serum anti-spike IgG that inhibited spike ACE-2 binding and neutralized both wild-type and delta variant virus. Both adjuvanted vaccine formulations protected juvenile cats against virus shedding from the upper respiratory tract and viral replication in the lower respiratory tract and hearts. These promising data warrant ongoing evaluation of the vaccine's ability to protect cats against SARS-CoV-2 infection and in particular to prevent transmission.

Whereas multiple vaccine types have been developed to curb the spread of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) among humans, there are very few vaccines being developed for animals including pets. To combat the threat of human-to-animal, animal-to-animal and animal-to-human transmission and the generation of new virus variants, we developed a subunit SARS-CoV-2 vaccine which is based on recombinant spike protein extracellular domain expressed in insect cells then formulated with appropriate adjuvants. Sixteen 8-12-week-old outbred female and male kittens (n=4/group) were randomly assigned into four treatment groups: Group 1, Antigen alone; Group 2, Sepivac SWE™ adjuvant; Group 3, aluminum hydroxide adjuvant; Group 4, PBS administered control animals. All animals were vaccinated twice at day 0 and 14, intramuscularly in a volume of 0.5 mL (Groups 1-3: 5 µg of Spike protein). On days 0 and 28 serum samples were collected to evaluate anti-spike IgG, inhibition of spike binding to angiotensin-converting enzyme 2 (ACE-2), neutralizing antibodies to Wuhan-01 SARS-CoV-2 D614G (wild-type) and Delta variant viruses, and whole blood for hematology studies. At day 28, all groups were challenged with SARS-CoV-2 wild-type virus 106 TCID50 intranasally. On day 31, tissue samples (lung, heart, and nasal turbinates) were collected for histology, viral RNA detection and virus titration. Parameters evaluated in this study included safety, immunogenicity, and protection from infection with wild-type SARS-CoV-2 virus. After two immunizations, both vaccines induced high titers of serum anti-spike IgG, ACE-2 binding inhibitory and neutralizing antibodies against both wild-type and Delta variant virus in the juvenile cats. Both subunit vaccines provided protection of juvenile cats against virus shedding from the upper respiratory tract, and against viral replication in the lower respiratory tract and hearts. These promising data warrant ongoing evaluation of the vaccine’s ability to protect cats against SARS-CoV-2 Delta variant and in particular to prevent transmission of the infection to naïve cats, before proceeding with large-scale field trials.