Aims & Objectives: Significant shares of PICU admissions are caused by diseases easily prevented with complete immunization status. This study has two primary objectives: 1) to determine the prevalence of under-immunized children upon admission to the PICU in Hanoi, Vietnam and 2) to understand the collection method of immunization status of children admitted to the PICU. Methods This study is a prospective, observational study conducted in the PICU at the National Hospital for Pediatrics in Hanoi, Vietnam from June 2017 to December 2017 sampling vaccination status of pediatric patients aged 0–18 years old. Multilevel analysis using SPSS statistics were undertaken to analyze results. Results We present data from 100 patients to illustrate that a majority of patients are under-vaccinated (32% to 89% depending on the vaccine), or their parents are unsure of their vaccination status (10% to 25% depending on the vaccine). PIM 2 risk scores of mortality ranged from 0.1%-95.6% (N=100, mean: 30.827, standard deviation: 26.1591). When corrected for age, univariate ANOVAs analyzing PIM 2 risk scores with vaccination status trended to significance (F39=1.566, p=.060) but only children who were not vaccinated for measles had a significant increase in PIM 2 scores (F39=8.957; p=.004). Length of PICU duration was significantly increased when examined against vaccination coverage and corrected for age (F16=3.408 p=.034). Conclusions Understanding the risk factors, etiologies and outcomes of vaccination-related diseases may help guide routine clinical management and prioritize vaccination campaigns on both a governmental and public health level. This underlines the importance of collecting vaccination information for every patient upon admission.