Influenza remains a significant public health burden in India, causing seasonal outbreaks and substantial morbidity across all age groups. Despite available effective vaccines, uptake remains low, and comprehensive safety and immunogenicity data for quadrivalent influenza vaccines in Indian populations are limited. This open-label phase III study evaluated the immunogenicity and safety of a quadrivalent inactivated split-virion influenza vaccine (QIV) in participants aged 6 months and older across five Indian sites. Participants received one or two 0.5 mL doses based on age and prior vaccination history. A total of 401 participants were enrolled in the study. Geometric mean titers increased from baseline across all age groups for all four strains. Hemagglutination inhibition (HAI) geometric mean titer ratios (GMTRs) comparing post-vaccination to baseline values showed higher responses to A/H1N1 in adults aged 18 years and older, while A/H3N2 responses were similar across age groups. Younger participants demonstrated higher GMTRs for B/Yamagata and B/Victoria strains. Seroconversion rates at day 29 were generally highest against A/H1N1 across all ages. Solicited injection site reactions were comparable among age groups, though younger participants reported fewer local reactions. No vaccine-related serious adverse events occurred. These findings demonstrate that QIV induced HAI titer increases in pediatric populations comparable to or somewhat higher adult responses against all four vaccine strains. QIV immunization against influenza was generally safe and well tolerated in both adults and children.Clinical Trials Registry - India: CTRI/2021/11/037841.
Folegatti et al. (2026) studied this question.