Newborn girls were significantly less likely than boys to receive both the recommended vitamin K (VK) injection and hepatitis B vaccine (HBV), leaving them vulnerable to potentially fatal bleeding and chronic liver disease, respectively.
But parental VK and HBV refusal rose significantly among both sexes from 2018 through 2025.
For the study, researchers from the Children’s Hospital of Philadelphia (CHOP) and the University of Pennsylvania analyzed rates of parental decline or acceptance of VK prophylaxis (prevention) and HBV administration among infants born at 35 weeks’ or more gestation at three centers in a single healthcare center.
The findings were published this week in JAMA Network Open.
No circumcisions were done for newborns not given VK
Of 93,163 newborns, 777 didn’t receive VK prophylaxis (8.3 newborns per 1,000 births), and 9,400 didn’t receive HBV (100.9 newborns/1,000 births). HBV wasn’t given to 646 of 777 newborns (83%) whose parents also declined the VK injection.
Newborn girls were twice as likely as boys to not receive VK prophylaxis (adjusted odds ratio [aOR], 2.03). VK refusal rose significantly among both boys and girls. Among girls, rates of VK prophylaxis refusal increased by 1.37 newborns per 1,000 female births each year, for an absolute incidence of 9.6 per 1,000 births in 2018 (55/5,708 births) and 19.8 per 1,000 births in 2025 (113/5,706).
Parental decline of VK prophylaxis for infant boys climbed by 0.75 newborns per 1,000 male births each year, for an absolute incidence of 4.0 per 1,000 births in 2018 (23/5,820) and 10.1 per 1,000 in 2025 (60/5,934).
Female sex was also tied to slightly higher rates of HBV nonreceipt (aOR, 1.06), although HBV refusal rose significantly among both girls and boys. Among girls, HBV refusal rates jumped by 10.3 newborns per 1,000 female births per year, for an absolute incidence of 86.4 per 1,000 in 2018 (493/5,708 births) and 173.7 per 1,000 in 2025 (991/5,706 births).
Among newborn boys, the rate of yearly HBV refusal climbed by 11.0 newborns per 1,000 male births, for an absolute incidence of 77.9 per 1,000 in 2018 (453/5,818 births) and 166.3 per 1,000 in 2025 (987/5,934 births).
Birth center, non-Hispanic maternal race, and public insurance coverage were linked to VK and HBV administration. Yearly circumcision rates ranged from 72% to 77%, and none were performed for newborns not given VK.
Sociocultural, religious, and individual factors
“In this cohort study, newborn female sex was associated with significantly lower odds of VK prophylaxis and HBV administration, with greater sex discordance for VK prophylaxis vs HBV,” the study authors wrote. “VK prophylaxis decline rates doubled between 2018 and 2025 among both sexes, but two-thirds of newborns not administered VK prophylaxis were female.”
As of late 2025, the Centers for Disease Control and Prevention no longer recommend routine newborn HBV administration. This change conflicts with American Academy of Pediatrics guidance and may confuse families, reinforce vaccine misinformation, and exacerbate declining vaccination rates.
They say that sociocultural, religious, and individual factors likely influence parental decisions to decline evidence-based newborn care, but data on such decision-making through a sex-specific lens is scarce. “Our centers have substantial baseline male circumcision rates, and we speculate that desire for circumcision may influence VK prophylaxis acceptance among otherwise hesitant parents of male newborns,” they wrote.
While differences in HBV administration are poorly described, low- and middle-income countries have reported sex disparities in childhood vaccination, the researchers noted.
“As of late 2025, the Centers for Disease Control and Prevention no longer recommend routine newborn HBV administration,” they wrote. “This change conflicts with American Academy of Pediatrics guidance and may confuse families, reinforce vaccine misinformation, and exacerbate declining vaccination rates.”
Study limitations include analysis in a single health system, residual confounding stemming from unmeasurable factors (eg, parental beliefs), and the inability to link vaccination status and morbidities (eg, VK deficiency bleeding [VKDB]) after the birth hospitalization.
“Further studies should address sex-specific rates of newborn VK prophylaxis and HBV administration, VKDB, and neonatal hepatitis B infection nationally,” the authors concluded. “Innovative strategies are required to reduce disparities in VK prophylaxis and HBV administration and limit life-threatening morbidity among female newborns.”
