It would certainly be interesting to see how often the mother was producing antibodies for things that the father wasn't (more mundane infection vectors are one of the ideas presented at my link, if baby, mother and father are all sick, you don't have much evidence of the saliva being important).
http://www.skepticalob.com/2015/09/mothers-and-babies-commun...
It would certainly be interesting to see how often the mother was producing antibodies for things that the father wasn't (more mundane infection vectors are one of the ideas presented at my link, if baby, mother and father are all sick, you don't have much evidence of the saliva being important).