Influenza A(H3N2) Antibody Responses to Standard-Dose Versus Enhanced Influenza Vaccine Immunogenicity in Older Adults and Prior Season's Vaccine Status

Abstract

Abstract Background Annual influenza vaccination is recommended for older adults but repeated vaccination with standard-dose influenza vaccine has been linked to reduced immunogenicity and effectiveness, especially against A(H3N2) viruses. Methods Community-dwelling Hong Kong adults aged 65–82 years were randomly allocated to receive 2017–2018 standard-dose quadrivalent, MF59-adjuvanted trivalent, high-dose trivalent, and recombinant-HA quadrivalent vaccination. Antibody response to unchanged A(H3N2) vaccine antigen was compared among participants with and without self-reported prior year (2016–2017) standard-dose vaccination. Results Mean fold rise (MFR) in antibody titers from day 0 to day 30 by hemagglutination inhibition and virus microneutralization assays were lower among 2017–2018 standard-dose and enhanced vaccine recipients with (range, 1.7–3.0) versus without (range, 4.3–14.3) prior 2016–2017 vaccination. MFR was significantly reduced by about one-half to four-fifths for previously vaccinated recipients of standard-dose and all 3 enhanced vaccines (β range, .21–.48). Among prior-year vaccinated older adults, enhanced vaccines induced higher 1.43 to 2.39-fold geometric mean titers and 1.28 to 1.74-fold MFR versus standard-dose vaccine by microneutralization assay. Conclusions In the context of unchanged A(H3N2) vaccine strain, prior-year vaccination was associated with reduced antibody response among both standard-dose and enhanced influenza vaccine recipients. Enhanced vaccines improved antibody response among older adults with prior-year standard-dose vaccination.