The anti-vaccine movement hasn’t only resulted in more childhood cases of preventable diseases, like measles and whooping cough. Doctors are also seeing increased rates of problems that are easily avoidable through shot-based treatments. This time, it’s the vitamin K shot we give babies to prevent dangerous internal bleeding.

The body uses vitamin K (specifically vitamin K1 and K2) to synthesize proteins needed for blood coagulation. Vitamin K allows these proteins to bind to calcium: If they’re unable to do so, injuries can result in severe, uncontrolled bleeding.

Deficiency is rare in healthy adults who maintain a balanced diet, but newborns are at higher risk. While K1 and K2 are abundant in leafy vegetables and dairy and meats, gut bacteria typically produce most of the body’s necessary vitamin K. Infants are still growing and developing a diverse gut microbiome. Since 1961 pediatricians have routinely provided a vitamin K shot to prevent a deficiency.

As the anti-vaccination movement has ramped up, more and more parents are declining the shot for their babies. Dr. Robert Sidonio, a hematologist at Emory University, told CBS News that many parents were waiving off the vitamin K shot because of mistaken belief that vitamin K shots lead to leukemia — which stems from some bad studies in the early 1990s, like this one and this one.

Pay no attention to posters like these.

Although this link has been fundamentally debunked, some parents are still suspicious of the vitamin K shot.

Sidonio said the CDC was seeing an “alarming” upward trend in infants experiencing internal bleeding. For example, in birthing centers near Vanderbilt University, 28 percent of parents who had just given birth refused to let their baby get the vitamin K shot. A paper in the Journal of Emergency Medicine describes a case in which Ohio doctors encountered a 10-week-old boy suffering from “profound anemia and intracranial bleeding” due to vitamin K deficiency. Bleeding around the brain can be fatal and result in permanent brain damage even if the child survives.

So make sure your kids are getting their shots, people. Seriously.

Photos via Flickr user Honorem Veritas, James Gathany, Judy Schmidt, USCDCP