Real-World Safety Profile of an Indian Trivalent Influenza Vaccine: Results From a Multi-centre Post-marketing Surveillance Study

Background: The global transition from quadrivalent influenza vaccine (QIV) to trivalent influenza vaccine (TIV) follows the effective disappearance of the influenza B/Yamagata lineage from global surveillance since March 2020. India aligned with this transition for the Northern Hemisphere (NH) 2025-26 season. This study evaluates real-world TIV safety in a predominantly paediatric Indian cohort and documents vaccine utilisation patterns within the study network. Methods: Retrospective, observational, open-label, single-arm, multi-centre post-marketing surveillance study (N = 4,881; 577 sites; age ≥6 months). The primary safety and tolerability analysis was conducted in TIV recipients (n = 4,474); the remaining 407 subjects received QIV and were not included in the primary safety analysis. Safety was assessed on a routinely used post-marketing surveillance rating scale (Excellent/Good/Fair/Poor). All adverse events following immunisation (AEFIs) were solicited and reported as temporally associated observations; no formal causality assessment was performed. Results: Of 4,881 total subjects, 4,474 (91.7%) received TIV; the remaining 407 (8.3%) received QIV. The TIV cohort was predominantly paediatric (61.0% aged ≤18 years; 36.0% infants aged six to <7 months and seven to 12 months combined). Among TIV recipients, safety was rated Excellent or Good by 99.13% of patients and 99.33% of physicians. AEFIs occurred in 314 TIV recipients (7.02%), all mild and self-limiting. Age-stratified AEFI rates ranged from 1.01% to 2.37% across all subgroups, with no serious AEFIs in any age group. Additionally, this study substantiates the safety of TIV in pregnancy. Conclusions: TIV demonstrated an excellent real-world safety and tolerability profile in 4,474 TIV recipients across 577 Indian clinical sites, with high TIV uptake (91.7%), only mild and self-limiting adverse events, no serious events, and minimal site-level variability. These findings support its continued use in routine and large-scale public health immunisation programs, while larger studies are warranted in specific subpopulations.