The future of neonatal BCG.

We hypothesise that neonatal BCG (Bacillus Calmette-Guérin) might be used to adapt to a new phase in the history of human births. Among most mammals, the placenta is not effective at transferring antibodies to the fetus: antibodies are transferred immediately after birth via the colostrum. Among humans (and other mammals with hemochorial placentas) the transplacental transfer of antibodies (namely IgG) is effective. In humans, foetal concentrations of IgG sub-classes approximate to maternal concentrations at 38weeks and continue to increase thereafter. These facts explain inter-species differences regarding the basic needs of neonates. Among most mammals, the early colostrum is, strictly speaking, vital. Among humans, the main questions are about the bacteriological environment in the birthing place and how familiar it is to the mother. Today, most human beings are born in unfamiliar bacteriological environments characterized by a low microbial diversity. The effects of clinical environments may be amplified by the use of antibiotics and birth by caesarean, i.e. by-passing the bacteriologically rich perineal zone. There is already an accumulation of data confirming that the maturation of a balanced Th1/Th2 immune response is affected by the mode of delivery. There is also an accumulation of epidemiological studies detecting risk factors in the perinatal period for health conditions such as type 1 diabetes (and other autoimmune diseases), atopy, autism and obesity. In such a context there are reasons to plan randomized controlled trials with long term follow-up of the effects of BCG given immediately after birth, as a modulator of Th-1/Th-2 responses. A follow-up period in the region of 6-10years would be long enough to evaluate the prevalence of several nosologically well defined diseases. These studies would be ethically acceptable, since BCG is the only infancy vaccine that has been evaluated through randomised controlled trials with long term follow-up. Furthermore, whatever the standard of living of the populations and the research protocols, concordant results suggest that BCG has positive non-specific long term effects on health. Meanwhile, some simple adaptive practices are possible, such as, after a caesarean section, wrapping the neonate in clothes recently worn by the mother and, occasionally, putting the neonate in the arms of a person who is cohabiting with the mother.