Influenza A Virus at the Exhibition Swine-Human Interface in the USA

In the USA, zoonotic influenza A virus (IAV) transmission occurs frequently in youth who exhibit swine at agricultural competitions, presenting an ongoing pandemic risk. However, active surveillance in this high-risk human population is lacking.

To address this gap, we enrolled 711 youth participants at nine swine exhibitions during 2019-2021 and collected 700 nasal swabs and 400 serum samples. We assessed the neutralizing antibody titers of enrollees against eight influenza A H1 and H3 variant candidate vaccine viruses (CVVs) recommended by the World Health Organization.

We found that the highest neutralizing titers are not necessarily associated with the specific viruses which are most prevalent in exhibition swine during the same time period. The geometric mean titers of the cohort were low against the Cluster IV-A (clade 3.1990.4.a) CVV, which we determined to be the most prevalent HA lineage circulating in exhibition swine during 2020-2021 based on simultaneous IAV surveillance in swine (n = 430 genome sequences).

The relatively low neutralizing antibody levels in this high-risk population with intense exposure to livestock indicates that sustained outreach and monitoring is needed. Continued monitoring of IAVs in both swine and humans can inform viral risk assessments and provide considerations for candidate vaccine virus selection.