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.