Antibody responses against influenza A decline with successive years of annual influenza vaccination: results from an Australian Healthcare Worker cohort

Abstract

Influenza vaccine effectiveness and immunogenicity can be compromised with repeated vaccination. We assessed immunological markers in a cohort of healthcare workers (HCW) from six public hospitals around Australia during 2020-2021. Sera were collected pre-vaccination and ~14 and ~ 180 days post-vaccination and assessed in haemagglutination inhibition assay against egg-grown vaccine and equivalent cell-grown viruses. Responses to vaccination were compared by the number of prior vaccinations. Baseline sera were available for 595 HCW in 2020 and 1031 in 2021. 5% had not been vaccinated during five years prior to enrolment and 55% had been vaccinated every year. Post-vaccination titres for all vaccine antigens were lowest among HCW vaccinated in all 5-prior years and highest among HCW with 0 or 1 prior vaccinations, even after adjustment. This was observed for both influenza A subtypes and was dependent on pre-vaccination titre. Expanded cohorts are needed to better understand how this translates to vaccine effectiveness.; Competing Interests: Declarations Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: AF, AK, SGS report financial support was provided by National Institutes of Health. AF reports funding/grants from Sanofi Aventis, France. HM reports funding/grants from bioCSL, Pfizer Inc, GlaxoSmithKline. PW reports funding/grants from GlaxoSmithKline Inc, Krystal Biotech, Inc. Vertex Pharmaceuticals, Sanofi. SGS reports consulting for Pfizer Inc, Moderna Inc, Seqirus, Evo Health and Novavax. ACC, CCB are previous Chairs of the Australian Technical Advisory Group on Immunisation (ATAGI). The opinions in this study may not reflect the policy of ATAGI or the Australian Government regarding COVID-19 vaccines.