Four infants in Tennessee developed an exceedingly rare bleeding disorder, after their parents turned down the administration of standard vitamin K injections. The cluster of illness, reported this week by the Centers for Disease Control and Prevention (CDC), highlights the ongoing risks of parents either refusing or delaying preventive injections — like vitamin K or MMR vaccinations — among infants and children.

Since around 1961, doctors in the US have used vitamin K injections to prevent Vitamin K deficiency bleeding (VKDB) in newborns. Infants are born with low levels of vitamin K, which is vital in helping blood coagulate, and they don't obtain sufficient levels of the vitamin during breastfeeding. That puts them at an increased risk of hemorrhage, which is precisely why the American Academy of Pediatrics has long recommended injections of the vitamin at birth: infants who don't receive it are 81 times more likely to experience VKDB.

"Fears that the injection increases the risk of leukemia."

All of the infants in this illness cluster survived, though longterm neurodevelopmental repercussions (three of them suffered intracranial hemorrhage) remain a possibility. The CDC's research also revealed that a whopping 28 percent of infants born at birthing centers in Nashville didn't receive a vitamin K injection in 2013, compared to 3.4 percent of infants born at one Nashville hospital.

Some parents of the babies in question said that they declined a vitamin K injection because of fears — which have no scientific backing — that the injection increases the risk of leukemia. Others cited a concern over exposing their child to excessive toxins. The CDC is now working to determine whether cases of VKDB, at least in Tennessee, have been occurring at an increased rate in recent years, or are being underreported.