Safety profile of India's influenza vaccine in a large-scale corporate vaccination drive.

Seasonal influenza causes substantial morbidity, mortality, and productivity losses worldwide, and although annual vaccination is recommended for adults, coverage in India remains low; corporate vaccination drives may improve access and uptake among working-age adults. We evaluated the safety profile of an inactivated quadrivalent influenza vaccine administered during a large-scale corporate vaccination program in India. This observational post-marketing surveillance study was conducted during a multi-center drive at Maruti Suzuki India Ltd. where consenting employees aged ≥18 y received a single 0.5 mL intramuscular dose of inactivated influenza vaccine (Vaxiflu-4, Zydus Vaccines). Recipients were observed for 30 min post-vaccination for immediate reactions and instructed to report adverse events (AEs) occurring within 7 d post-vaccination using a standardized reporting form or helpline; AEs were classified as systemic, local, or serious and summarized descriptively. Among 9,000 vaccinated employees (88% male; 75% aged ≤40 y), no serious AEs were reported. Systemic AEs were infrequent, including fever in 13 recipients (0.14%), flu-like symptoms in 9 (0.10%), and headache in 3 (0.03%), all of which were self-limiting. Local AEs were rare, with soreness at the injection site reported by 18 participants (0.20%); no swelling or redness was reported. One case of frozen shoulder (0.01%) was recorded and assessed as unrelated to vaccination. Overall, the inactivated quadrivalent influenza vaccine (Vaxiflu-4) demonstrated a favorable safety profile in this large corporate setting, with very low rates of mild systemic and local AEs and no serious vaccine-related events, supporting workplace influenza vaccination programs as a feasible strategy to improve adult immunization coverage in India.