An inactivated influenza D virus vaccine protects guinea pigs from infections and contact transmission caused by homologous challenge.

Influenza D virus (IDV) was first isolated from pigs in 2011 which caused the bovine respiratory disease and economic losses. This study aimed to develop an inactivated vaccine to protect against IDV using guinea pigs as an animal model. Vaccinated guinea pigs exhibited seroconversion with hemagglutination inhibition titers ranging from 1: 320 to 1: 640 and neutralizing antibody levels reaching 1: 2560 after booster immunity. In the vaccinated guinea pigs, viral titers were detected in the nasal lavage fluids from days one to seven, showing a significant difference from the control group. Peak viral shedding of approximately 10⁶ TCID₅₀/mL was measured in the nasal turbinate and nasal washes from days one to five. In contact transmission experiments, non-vaccinated guinea pigs that lived with the infection group were more likely to become infected than those in the vaccinated group. These results demonstrate that the inactivated IDV vaccine protected guinea pigs from contact transmission caused by homologous challenge. Our study provides a new choice for developing IDV vaccines to protect animals from IDV infections.