Single immunization with an influenza hemagglutinin nanoparticle-based vaccine elicits durable protective immunity.

Vaccination is the most effective strategy to combat influenza. Ideally, potent and persistent vaccine effects would be induced with a single vaccine dose. Here, we designed a virus-like particle (VLP)-based vaccine presenting multiple copies of the influenza hemagglutinin (HA) from A/Puerto Rico/8/1934 (PR8HA-VLP) and examined its immunogenicity and protective efficacy in ferrets. Serum-neutralizing antibodies were effectively induced against the homologous virus at 3-week post-vaccination with a single dose of PR8HA-VLP with or without adjuvants. When the single-immunized ferrets were challenged with the homologous virus, virus replication in the nasal mucosa was significantly reduced. Long-term monitoring of serum titers revealed that after adjuvanted vaccination with PR8HA-VLP, neutralizing antibodies were retained at similar levels 20- to 183-week post-vaccination, although a 4- to 8-fold titer decline was observed from 3- to 20-week post-vaccination. Boost immunization at 183 weeks after the first immunization elicited higher neutralizing antibody titers than those at 3 weeks after the initial immunization in most of the animals. These results confirm that nanoparticle-based vaccines are a promising approach to effectively elicit durable multiyear neutralizing antibody responses against influenza viruses.