Safety Profile of GSK’s Inactivated Quadrivalent Seasonal Influenza Vaccine in Belgium, Germany and Spain: Passive Enhanced Safety Surveillance Study for the 2019/2020 Influenza Season

INTRODUCTION: Seasonal influenza infects millions annually in Europe. Annual influenza vaccination is the most effective measure to reduce the risk of infection and its complications, especially among young children and older adults. OBJECTIVE: We assessed adverse event (AE) frequency after receiving GSK’s inactivated quadrivalent seasonal influenza vaccine (IIV4). METHODS: A passive enhanced safety surveillance study was conducted in Belgium, Germany, and Spain. Adults who had received GSK's IIV4 or the parent(s)/guardian(s)/legally acceptable representative(s) of children given the vaccine were invited to complete an adverse drug reaction (ADR) card to document AEs experienced within 7 days post vaccination. RESULTS: A total of 1082 participants (51.6% females) received GSK's IIV4, including 115 children < 9 years of age who received two doses. The ADR card return rate was 97.0% (n = 1049) after dose 1 and 100% (n = 115) after dose 2. All participants in Belgium and Germany were adults. In Spain, 71.2% were children. After dose 1, 39.2% reported one or more AE. The most frequent AEs category was "general disorders and administration site conditions” (GDASC). AEs were most frequently reported in adults aged 18–65 years (47.2%), followed by children aged 6 months–17 years (38.1%), and adults aged > 65 years (31.6%). After dose 2, 7.8% reported one or more AE, and GDASC was again the most frequent AE category. There were no serious AEs related to GSK's IIV4 within 7 days post vaccination. CONCLUSION: No serious AEs related to GSK’s IIV4 within 7 days post vaccination were reported. This study supports the favourable risk–benefit safety profile of GSK’s IIV4. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40264-021-01121-8.