An inactivated split-virion trivalent influenza vaccine (IIV3; Vaxigrip®, Sanofi Pasteur) has been available globally since 1968. Here, we describe the results of an open-label, post-licensure trial (EudraCT no. 2014-005078-12) to confirm the immunogenicity and safety of the Southern Hemisphere 2015 formulation of IIV3. Adults 18-60 years of age and > 60 years of age (60 per age group) received a single 0.5-ml intramuscular injection of IIV3. Between baseline and day 21 after vaccination, hemagglutination inhibition (HAI) titers for each strain in IIV3 increased, on average, by at least 11-fold for younger adults and at least 5-fold for older adults. After vaccination, 89%-100% of the younger adult participants and 90%-98% of the older adult participants attained seroprotection (HAI titer ≥ 40) for each strain. Also, 66%-81% of younger adults and 45%-63% of older adults seroconverted or had a significant increase in HAI titer for each strain. For both age groups, these post-vaccination immune responses exceeded the criteria of the Committee for Human Medicinal Products former Note for Guidance for influenza vaccines. No serious adverse events were reported, and no new safety signals were detected. In conclusion, this study confirmed that the Southern Hemisphere 2015 formulation of IIV3 was well tolerated, highly immunogenic, and met the criteria for influenza vaccine efficacy and safety.
Keywords: Southern Hemisphere; immunogenicity; safety; trivalent inactivated influenza vaccine.