Claeys, CarineChandrasekaran, VijayalakshmiGarcía-Sicilia, JoséPrymula, RomanDíez-Domingo, JavierBrzostek, JerzyMarès-Bermúdez, JosepMartinón-Torres, FedericoPollard, Andrew JRůžková, RenataCarmona Martinez, AlfonsoUlied, AngelsMiranda Valdivieso, MarianoFaust, Saul NSnape, Matthew DFriel, DamienOllinger, ThierrySoni, JyotiSchuind, AnneLi, PingInnis, Bruce LJain, Varsha K2023-01-252023-01-252019http://hdl.handle.net/10668/13092It has not yet been demonstrated whether 2 doses of inactivated quadrivalent influenza vaccine (IIV4) prime a booster response in infants. We evaluated the anamnestic immune response to an IIV4 in children 17-48 months of age. Children were randomized to 2 doses of IIV4 or control in the primary phase III study (NCT01439360). One year later, in an open-label revaccination extension study (NCT01702454), a subset of children who received IIV4 in the primary study (primed group) received 1 IIV4 dose and children who received control in the primary study (unprimed) received 2 IIV4 doses 28 days apart. The primary objective was to evaluate hemagglutination inhibition (HI) antibody titers 7 days after first IIV4 vaccination in the per-protocol cohort (N = 224 primed; N = 209 unprimed). Neutralizing and antineuraminidase antibodies were also measured. Safety was analyzed in the total vaccinated cohort (N = 241 primed; N = 229 unprimed). An anamnestic response was observed in primed children relative to unprimed controls, measured by age-adjusted geometric mean HI titer ratios against strains homologous (A/H1N1: 9.0; B/Victoria: 3.9) and heterologous (A/H3N2: 2.7; B/Yamagata: 6.7) to those in the primary vaccination series. The anamnestic response in primed children included increases in neutralizing antibodies (mean geometric increase: 5.0-10.6) and antineuraminidase antibodies (4.9-8.8). No serious adverse events related to vaccination were reported. In this study, 2-dose priming with IIV4 induced immune memory that was recalled with 1-dose IIV4 the following year to boost HI, antineuraminidase and neutralizing antibodies, even though the IIV4 strain composition partially changed.enAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/Antibodies, NeutralizingAntibodies, ViralChild, PreschoolDrug-Related Side Effects and Adverse ReactionsFemaleHemagglutination Inhibition TestsHumansImmunologic MemoryInfantInfluenza VaccinesInfluenza, HumanMaleNeutralization TestsVaccines, Inactivatedresearch article30325891open access10.1097/INF.00000000000022171532-0987PMC6344072http://links.lww.com/INF/D323https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6344072/pdf