Immunogenicity, Reactogenicity and Safety of Quadrivalent and Trivalent Influenza Vaccines

A total of 4,659 adults aged 18 years or older were randomized to receive a single dose of inactivated quadrivalent influenza vaccine (IIV4) from one of three production lots or an inactivated trivalent influenza vaccine (IIV3) containing either a B/Victoria or B/Yamagata strain. The objectives were to evaluate the immunogenicity, reactogenicity and safety of both formulations, as well as lot-to-lot consistency of IIV4. A priori, non-inferiority for IIV4 against IIV3 for the three shared strains was considered demonstrated if the 95 percent confidence interval (CI) upper limit for the geometric mean titer (GMT) ratio was less than or equal to 1.5 and for the seroconversion difference was less than or equal to 10 percent.

Consistent immunogenicity was demonstrated for all three IIV4 lots. IIV4 was non-inferior to IIV3 for the shared vaccine strains (A/H1N1, A/H3N2 and the shared B strain) and, as expected, was superior for the added alternate-lineage B strains. IIV4 elicited robust immune responses against all four vaccine strains, with seroconversion rates of 77.5 percent (A/H1N1), 71.5 percent (A/H3N2), 58.1 percent (B/Victoria) and 61.7 percent (B/Yamagata). The reactogenicity and safety profile of IIV4 was consistent with IIV3.

The investigators concluded that IIV4 provided superior immunogenicity for the additional B strain compared with IIV3, without interfering with antibody responses to the three shared antigens or affecting safety.