More parents are refusing a shot typically given at birth to reduce the risk of infant bleeding, a study recently published in the Journal of the American Medical Association found.

An injection of vitamin K, which helps with blood clotting, within six hours of birth has been a standard practice in the U.S. since 1961.

Since babies are born with low levels of the vitamin, they are more prone to serious bleeding, especially in the brain and gastrointestinal tract, according to the Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics (AAP).

Since implementing widespread use of the shot, the U.S. has seen a significant decrease in infant bleeds caused by vitamin K deficiency, according to the CDC. Increased hesitancy around vaccination, however, has led to an increasing number of parents opting out, especially after the COVID-19 pandemic and the increased public scepticism of pediatric preventive care that followed.

The latest study, "Trends in Vitamin K Administration Among Infants," was published in JAMA on Dec. 8. Using electronic medical record data, the study's authors reviewed more than 5 million births at over 40 hospitals across all 50 states between 2017 and 2024. The number of infants who did not receive the shot at birth rose from 2.92% in 2017 to 5.18% in 2024, according to the report. The largest acceleration occurred after 2020.

Parents refusing the shot often expressed concerns about injection pain, potential adverse effects and doubts that it's necessary, said the study. However, changes to acceptance rates began in 2019, the study noted, meaning COVID-19-related medical scepticism has not been the sole source of changing attitudes.

Why is vitamin K given to infants?

Since 1961, the AAP has recommended that a single shot of vitamin K be given at birth to protect against bleeding. All babies are born deficient in vitamin K, which is vital to blood clotting, and cannot form what are called clotting factors, or substances in the body that help stop bleeding naturally.

Vitamin K deficiency can cause serious, life-threatening bleeding in infants up to six months of age, according to the CDC. Normal sources of nutrition for newborns, including breast milk, do not contain enough vitamin K to make up for this deficiency in the early months of life.

A single shot given within hours of birth ensures babies have enough of the vital nutrient to handle any potential bleeding in the immediate future. According to the CDC, newborns who do not get a vitamin K shot are 81 times more likely to develop severe bleeding than those who do get the shot.

"Waiting to see if your baby needs a vitamin K shot may be too late," the CDC webpage says. "Babies can bleed into their intestines or brain, where parents can't see the bleeding to know that something is wrong. This can delay medical care and lead to serious and life-threatening consequences."

Why are more parents refusing?

Vaccine hesitancy and misconceptions as to the level of risk associated with vitamin K deficiency bleeding are the likely culprits behind refusal rates, said Dr. Ivan Hand, director of neonatology at NYC Health + Hospitals Kings County.

"I think it's sort of a general mistrust in our country that's grown in the last 10 years or so," he told USA TODAY. "I think it's a combination of things. There's been more of an emphasis on 'natural' birth and some parents think, 'it's not natural for my baby to get a shot of vitamin K at birth.' As well as trying to de-medicalise the birthing process and I think just a general mistrust."

A 2022 policy statement by the AAP, co-authored by Hand, found that parental refusal of the shot was associated with a lack of understanding of the need for vitamin K, belief that it was unnecessary, concern about the injection pain and concern related to the preservative in the formulation.

Some hesitant parents point to misinformation that has proliferated from a since-debunked 1990 study linking vitamin K to childhood cancer, while others believe that a "natural" birth with minimal or no interventions was healthiest for their babies, according to the policy statement. Some incorrectly believe the shot to be a vaccine and express concerns consistent with vaccine hesitation.

Births outside of hospital settings and without physicians were also associated with higher rates of refusal, the report said. "Outside influences include friends, celebrities, and even some health professionals," were also a factor.

"In some ways, we're victims of our own success, that people don't see this kind of bleeding anymore because almost all babies have gotten that shot," said Hand. "But if we fail to do that, we're going to see more and more cases of babies having bleeding, and those bleedings can be very significant, about half of them can relate to brain haemorrhage. So it's a very concerning thing that is easily prevented by babies just getting the shot."

This article originally appeared on USA TODAY: What is the vitamin K shot for and why are parents refusing it?