Serological response to avian influenza viruses among occupationally exposed population in Taiwan, a longitudinal cohort study, 2021-2023

The Taiwan Centers for Disease Control (TCDC) initiated longitudinal sero-epidemiological surveillance of avian influenza viruses (AIVs) targeting poultry workers exposed on affected farms since 2021. Convalescent-phase serum samples were collected from these workers 21-28 days post-outbreak identification. TCDC recontacted participants in subsequent years for repeat serological sampling. Hemagglutination inhibition (HI) assays were used to test against representative strains of AIV A/H5 2.3.4.4c and A/H5 2.3.4.4b. By the end of 2023, a 2-year cohort of 59 participants and a 3-year cohort of 61 participants were established. None of them had laboratory-confirmed infection. HI titers against AIV A/H5 2.3.4.4c remained low from 2021 to 2023. For AIV A/H5 2.3.4.4b, HI titer remained low from 2021 to 2022 but increased in more than half of the participants (60%, 72/120) in 2023. This change parallels the increasing AIV A/H5 2.3.4.4b burden indicated by increased outbreaks and warrants continuous monitoring.