Enhanced Safety Surveillance of GSK’s Inactivated Quadrivalent Seasonal Influenza Vaccine in Belgium, Germany, and Spain During the 2022/2023 Influenza Season

Background Seasonal influenza is prevented through annual vaccination, especially in children and older adults. These vaccines are annually updated based on World Health Organization recommendations and require continuous safety monitoring. Objective We assessed the frequency and severity of adverse events within 7 days of administering GSK’s inactivated quadrivalent seasonal influenza vaccine (IIV4) in Belgium, Germany, and Spain during the 2022/2023 influenza season. Methods In this enhanced safety surveillance study, adults who received GSK’s IIV4 and parents/guardians/legally acceptable representatives of vaccinated children (aged 6 months–17 years) were invited to complete adverse drug reaction cards reporting adverse events within 7 days post-vaccination. Results In total, 1332 participants (53.6% female) received at least one dose of GSK’s IIV4, including 43 children who received two doses. Overall, 97.8% of adverse drug reaction cards were completed and returned in the study. All participants in Belgium were adults, while 54.7% and 7.4% in Spain and Germany, respectively, were pediatric participants aged 6 months–17 years. After Dose 1, across all age groups, 49.8% of participants reported at least one adverse event. The most common adverse events (cumulative frequency >5%) following Dose 1 were injection-site pain (37.6%), fatigue (15.0%), headache (13.2%), injection-site swelling (9.3%), myalgia (7.6%), and injection-site erythema (7.4%). Across all countries, adverse events were most common in adults aged 18–65 years (59.7%), followed by those aged 3–17 years (47.0%), >65 years (35.7%), and 6–35 months (23.5%). After Dose 2, 18.6% of participants reported at least one adverse event, with general disorders and administration site conditions again being the most frequent. Conclusions Across all age and risk groups for serious disease, no serious adverse events related to GSK’s IIV4 were reported within 7 days post-vaccination. This study supports and confirms the acceptable safety profile of GSK’s IIV4 across all recommended age groups. Clinical Trial Registration ClinicalTrials.gov number: not applicable. Graphical Abstract