Interferon alpha inhibits replication of a live-attenuated porcine reproductive and respiratory syndrome virus vaccine preventing development of an adaptive immune response in swine.

•Interferon alpha (IFN-α) was administered via an adenovirus vector as an adjuvant with live-attenuated PRRSV vaccine as a method to enhance immune response to the vaccine.•IFN-α inhibited replication of the vaccine virus and as a result there was no detectable adaptive immune response.•Although IFN-α did not have the desired adjuvant effect, the results further highlight the use of IFN-α as a treatment for PRRSV infection.