Clinical trial to assess immunogenicity of high-dose,adjuvanted, and recombinant influenza vaccines against cell-grown A(H3N2) viruses in adults 65 to 74 years, 2017–2018

BackgroundLicensed inactivated influenza vaccines (IIV) are recommended for persons aged ≥65 years, including trivalent high-dose IIV (HD-IIV3) and adjuvanted IIV (aIIV3); both are manufactured in eggs. Quadrivalent recombinant vaccine (RIV4) is produced without eggs. We conducted an exploratory study to compare immunogenicity of HD-IIV3, aIIV3 and RIV4 against cell-grown vaccine and circulating A(H3N2) viruses in 2017–18.MethodsEighty-nine adults aged 65–74 years participating in a 2-year, open-label immunogenicity trial (ClinicalTrails.gov: NCT02872311) were randomized 1:1:1 to receive HD-IIV3, aIIV3, or RIV4 after receipt of standard dose IIV3 in 2016–17. Serum was obtained at baseline and day 28 post vaccination. Microneutralization titers were determined using four cell-propagated A(H3N2) viruses: 2017–18 vaccine strain (clade 3C.2a), circulating viruses from clades 3C.2a1 and 3C.2a2, and ‘antigenically advanced’ clade 3C.3a (2019–20 vaccine strain). Active surveillance was conducted to identify influenza illnesses.ResultsPost vaccination geometric mean titer (GMT) against the vaccine strain was <1:60 in each group and <15% seroconverted. RIV4 generated a greater fold-rise (2.0, 95% CI 1.7–2.5) compared to HD-IIV3 (1.6, 95% CI 1.3–1.8). RIV4 generated higher post vaccination titers against 3C.2a1 and 3C.2a2 viruses, and the mean fold-rise after RIV4 was twice as high (3.3 and 3.5, respectively) relative to HD-IIV3 (1.4 and 1.6) and aIIV3 (1.7 and 1.6). Against the antigenically advanced 3C.3a virus, RIV4 generated a greater mean fold-rise (2.9, 95% CI 2.0–4.3) vs HD-IIV3 (1.3, 95% CI 1.1–1.6) and aIIV3 (1.7, 95% CI 1.3–2.1). Postvaccination titers against 3C.2a2 were ≥1:40 in 5 of 7 participants with PCR-confirmed A(H3N2) infection during the ensuing influenza season.ConclusionHigh-dose, adjuvanted, and recombinant vaccines generated suboptimal neutralizing antibody responses to the cell-grown vaccine strain, but RIV4 generated a greater cross-protective response against circulating and antigenically advanced viruses. Recombinant technology may contribute to more broadly protective influenza vaccines, and comparative effectiveness studies are needed.