I read this question before, "Do more antigens fused together in a subunit vaccine illicit a stronger immunigenecity effect?"

Then something comes on my mind: "What about a whole unit vaccine?" As we all know, a polyvalent vaccine has already common in poultry vaccine industry but there isn't any single company ever produced Infectious coryza and Avian Influenza together (based on what i searched on the internet).

So, i've been wondering, are the interaction between these two microorganisms has any negative effect such as not ellicit a strong immunogenicity effect or maybe there are some characteristics of both microorganisms which makes it difficult to produce when combined together.

Thank you