In the Netherlands, in numerous flocks, signs of immunosuppression have been observed which could be related to a subclinical outbreak of IBDV. A new reassortant IBD strain has been detected in some European countries and has been defined by HIPRA under the name UK2019 strain.

There are indications that the UK2019 strain has spread to other countries. For this reason, this study was initiated in order to have an indication of the spread of this new virus in the Netherlands and to investigate whether there is a relationship between its appearance and the currently used vaccine strategy.