Abstract
BACKGROUND/OBJECTIVES: Influenza poses a significant risk for young children, particularly those under five. Cell culture-derived influenza vaccines offer advantages in reducing adaptive changes and mitigating egg allergy concerns. SKYCellflu(®) quadrivalent has been in use since 2015, and this study aimed to assess its safety and influenza infections in children aged 6-35 months in South Korea. METHODS: A prospective cohort, non-interventional, multi-center post-marketing surveillance study was conducted from 2020 to 2024. This study presents data from the 2023-2024 influenza season on safety and influenza infections in children aged 6-35 months following SKYCellflu(®) vaccination. Safety was assessed based on adverse events (AEs) within 28 days post-vaccination, and influenza infections were assessed via phone calls or medical record screening. RESULTS: Among 333 safety set participants, 54.4% reported at least one AE, with most being mild to moderate. The cumulative incidence of influenza infections among 247 ad hoc subsets was 4.5%, and the incidence rate was 1.3 per 100 person-months (95% CI, 0.7-2.4) during the 2023-2024 influenza season. The two-dose regimen in vaccine-naïve infants aged 6-11 months showed a lower cumulative incidence of influenza infection rate (0.8% vs. 3.8%) and incidence rate (0.3 vs. 0.9 per 100 person-months) than the one-dose group (3.8%). No influenza-related hospitalizations occurred within the ad hoc subset. CONCLUSIONS: This study demonstrated a tolerable safety profile and the pattern of influenza infections following SKYCellflu(®) vaccination. Additionally, the two-dose regimen was associated with a lower incidence of influenza infections, suggesting potential benefits in enhancing protection among infants aged 6-11 months.