The Centers for Disease Control and Prevention notes that without the injection, babies are 81 times more likely during the first six months to suffer life-threatening bleeding in the brain or gut. ^[1] The rate of newborns missing the vitamin K shot within a day of birth in US hospitals jumped more than 57% from January through June 2026, according to an analysis of health records for over 1 million births nationwide by Truveta. ^[2] A study published in Nature Health in 2026 analyzed 8.1 million emergency department visits from the summers of 2023-2025, using de-identified electronic health records from Truveta member health systems across 19 eastern U.S. states, led by researchers at Harvard University's Center for Climate, Health, and the Global Environment and Boston University School of Public Health. ^[3] During the June 2025 heat wave, approximately 9.2% of all-cause emergency department visits were attributable to heat, corresponding to about 6,986 additional visits across 19 eastern U.S. states. ^[4] One in five infants who suffer severe bleeding will die, and without the shot, such bleeding occurs in one out of every 59 births. ^[5] The non-administration rate of the vitamin K shot was 2.5 times higher in the first half of 2026 than the average rate recorded from 2019 to 2024. ^[6] Amruta Nori-Sarma, lead author and deputy director of Harvard Chan C-CHANGE, said the study is a proof of concept for using near-real-time electronic health record data as actionable intelligence during an ongoing climate event, and that heat-related emergency visits showed only a modest decline between the June and August 2025 heat waves. ^[7]