The breadth of protection mediated by anti-N2 neuraminidase antibody responses relies on cross-reactive and not cross-inhibiting antibodies

Neuraminidase (NA) inhibition (NAI) titers have been identified as an independent correlation of protection against influenza. Few studies, however, have investigated the breadth of NA-based immune protection. Previously, we have reported that N2 NAs derived from human H3N2 viruses that circulated between 2009 and 2017 can be subdivided into four antigenic groups. Here, we immunized mice with recombinant soluble tetrameric NA from H3N2 strains representing those four antigenic groups or passively transferred N2 NA immune serum into naive mice to evaluate the breadth of protection against a heterologous HxN2 influenza virus challenge. We show that the breadth of protection goes beyond the breadth of NAI but still requires the presence of cross-reactive antibodies. Interestingly, in the absence of cross-reactive antibodies, the immunization of DBA/2J mice with heterologous NA was associated with an early onset of disease upon challenge with the reassortant HxNind11 or H2N2 A/Singapore/1/1957.