An 8-Year Prospective, Observational, Multi-centre Post-Marketing Safety Surveillance Study Conducted in South Korea (2014–2022) Following the Introduction of GSK’s Inactivated Quadrivalent Seasonal Influenza Vaccine (Fluarix Tetra) for Subjects Aged 6 Months and Older

Introduction Seasonal influenza is associated with substantial public health burden. The objective of this study was to assess the safety of inactivated quadrivalent seasonal influenza vaccine (IIV4, Fluarix Tetra, GSK, Belgium) in subjects aged ≥ 6 months in Korea. Methods This prospective, observational, non-comparative, multi-centre post-marketing surveillance study was conducted in Korea in subjects aged ≥ 3 years for 6 years (2014–2020) and extended to subjects aged 6–35 months for 4 years (2018–2022). Subjects received IIV4 in routine clinical practice according to local prescribing information. Adverse events (AEs) were recorded over 21 days post-vaccination. Results The group aged ≥ 3 years included 701 subjects (mean 31.97 years, range 3–86 years, 46.36% male), and the group aged 6–35 months included 687 subjects (mean 16.31 months, 47.02% male). In the group aged ≥ 3 years, 98 subjects (13.98%) reported 140 AEs, of which 42 events in 34 subjects (4.85%) were adverse reactions to vaccine (ARVs). Most of the ARVs were expected, mainly administration site reactions. There were seven mild unexpected ARVs. In the group aged 6–35 months, 248 AEs were reported in 149/687 subjects (21.69%). ARVs were reported in 25/687 subjects (3.64%, 29 events); one was considered unexpected. There were five serious AEs overall, none of which were considered related. Conclusion No safety concerns were found during this surveillance study of IIV4 in subjects aged ≥ 6 months in Korea. The findings of this study suggest IIV4 is safe and well tolerated for use in all age groups with a vaccine indication. Graphical Abstract