(269) Association between simultaneous vaccination with live and inactivated vaccines and risk of hospitalization for non-vaccine-targeted infections

Publication Number: 1259

Background: Recently published observational study have suggested that hospitalizations for non-vaccine-targeted infection (NTI) was increased when concurrent vaccination with inactivated vaccine compared to live vaccine alone in children.

Objectives: To investigate the risk of hospitalization associated with NTI 1624 months of age according to the type of the most recent vaccine (inactivated and/or live).

Methods: We performed a cohort study using linked databases of the Korea Immunization Registry Information System and National Health Insurance Service claims data. Subjects consisted of all toddlers born between Jan 1, 2013 and Dec 31, 2019, who had received at least 3 doses of DTaP-containing vaccine before 16 months of age to exclude the cases who had not completed recommended vaccination schedule. We assembled 3 cohorts of patients with live vaccine alone, inactivated vaccine alone and concurrent vaccination group according to the most recent received vaccine before the hospitalization for NTI after the index date (date of the last vaccination received before 16 months of age). Concurrent vaccination was defined as receiving both live and inactivated vaccines on the same day. Patients were followed from the index date until the earliest date of hospitalization for NTI, 25 months of age, death, or the end of the study. NTI includes any infection excluding vaccine-preventable diseases targeted by the national immunization program vaccines of Korea (e.g., infections of the gastrointestinal tract, urinary system, skin, or more). A Cox regression model was used to estimate hazard ratios (HRs) of hospitalization rates for NTI adjusting for comorbidity related to birth (e.g., small for gestational age), sociodemographic variables (e.g., sex), history of hospitalization for NTI, the number of outpatients, and influenza vaccination.

Results: Among those 3,047,566 toddlers, 50,367 had live vaccine alone (6.7%), 23,045 had simultaneous live and inactivated vaccine (0.8%) and 2,974,154 had inactivated vaccine alone (97.6%) as the most recent vaccine before NTI occurred. Among those, 1,558,721 (51.2%) were boys and 2,647,485 (86.9%) received at least 1 dose of influenza vaccine prior to censored date. Compared with live vaccine alone, the adjusted HR was 1.14 (95% CI = 1.101.18) for concurrent vaccination and 0.90 (95% CI = 0.950.97) for inactivated vaccine only group.

Conclusions: We found higher risk of NTI disease hospitalizations from age 1624 months among toddlers who received inactivated and live vaccines on the same day than those who received inactivated or live vaccine alone as the most recent vaccine prior to NTI. Further studies are warranted to explore the potential risks of hospitalization for NTI between various types of live and inactivated vaccines.