Antigenic assessment of the H3N2 component of the 2019-2020 Northern Hemisphere influenza vaccine.

The 2019–2020 Northern Hemisphere influenza vaccine includes antigens from 3c3.A H3N2 viruses; however, over half of circulating H3N2 viruses belong to subclade 3c2.A1b. Here, we analyze antibody responses elicited by the egg-adapted 3c3.A H3N2 vaccine strain in ferrets and humans. We find that this vaccine strain elicits antibodies that have reduced reactivity to a wild-type 3c3.A strain and very limited reactivity to 3c2.A strains, including the currently circulating 3c2.A1b strain. Vaccine mismatch and changes in antigenicity due to vaccine strain egg adaptation can affect seasonal influenza vaccine effectiveness. Here, Gouma et al. show that the egg-adapted 3c3.A H3N2 vaccine strain elicits antibodies with limited reactivity to a wildtype 3c3.A strain and currently circulating 3c2.A H3N2 strains.