This dual-cohort study spanning the US Veterans system and English health records demonstrates that severe infections requiring hospitalization accelerate frailty progression in adults over 65. Among 98% male US veterans (median age 74) and a more balanced English cohort (45% female, median age 76), those hospitalized for infections showed persistently higher frailty scores for up to five years post-infection. The most damaging infections were lower respiratory tract infections, sepsis, urinary tract infections, and meningoencephalitis. This finding illuminates a critical pathway by which acute infections catalyze long-term health decline in aging populations. The research addresses a significant gap in understanding how infectious episodes contribute to the frailty cascade—a key determinant of mortality and functional decline in older adults. The sustained nature of frailty acceleration, rather than a brief post-infection dip, suggests infections trigger lasting physiological changes affecting multiple organ systems. However, as this preprint awaits peer review, these findings require validation. The study's observational design cannot establish causation, and the predominantly male US cohort may limit generalizability. Nevertheless, this work reinforces infection prevention as a cornerstone of healthy aging strategies.