Background: Under the WHO's Global Action Plan for influenza vaccines, we conducted a phase 2-3 study of IVACFLU-S, a trivalent, seasonal inactivated influenza vaccine candidate.Methods: In the phase 2 portion of the study, 252 participants received one dose of 15 mcg hemagglutinin (HA) vaccine per strain or placebo. Following determination of safety, 636 additional participants were randomized in phase 3 to receive vaccine or placebo. Immunogenicity was assessed in a subset of the participants in the phase 3 study.Results: Higher proportion (70%) of participants in the IVACFLU-S arm reported solicited local adverse events (AEs) (p < .0001) as compared to placebo (25%). Mild injection site pain and tenderness were most common AEs seen in 55% and 60% of participants in the vaccine group. The solicited systemic AEs were comparable (p = .4149). The majority of solicited and unsolicited AEs were mild to moderate in severity. In the vaccine arm for the combined age group of 18-60 years of age, seroconversion against antigens A/H1N1, A/H3N2, and B was achieved in 70.3%, 76.1%, and 54.1% of participants respectively; seroprotection against antigens A/H1N1, A/H3N2, and B was achieved in 83.3%, 86.6%, and 60.3% of participants respectively; and the geometric mean fold rise for the hemagglutinin-inhibition (HI) antibody titers against antigen A/H1N1, A/H3N2, and B were 13.15, 11.85, and 5.87, respectively.Conclusion: This study demonstrates the local reactogenicity, other safety, and immunogenicity of IVACFLU-S, first domestically produced influenza vaccine in Vietnam.ClinicalTrials.gov number NCT03095599 (March 29, 2017).
Keywords: Trivalent seasonal influenza vaccine; Vietnam; immunogenicity; safety.