supposedly, every baby needs a Hep B shot on the day they are born,

because MAYBE their mother MIGHT have Hep B,

and somehow the Hep B test they give the mother MIGHT be a false negative,

and so the mother actually has Hep B, BUT the Hep B test didn't catch it.

and so the mother has Hep B, but the test can't find it, AND somehow the mother is NOT already giving Hep B to the baby while the baby is still inside the mother, because the blood is separate,

BUT during childbirth, the mother BLEEDS her Hep B infected blood all over the baby, thus exposing the baby to Hep B

But thanks to the marvels of Rockefeller Medicine,

your baby can now get a Hep B shot, that will somehow train your babies immune system how to fight the imminent Hep B infection that will certainly follow, before the Hep B infection itself takes hold.

Oh, and babies are also known to engage in highly risky behaviors, such as sharing dirty drug needles with sketchy prostitutes.