Intranasal parainfluenza virus-vectored vaccine expressing SARS-CoV-2 spike protein of Delta or Omicron B.1.1.529 induces mucosal and systemic immunity and protects hamsters against homologous and heterologous challenge

The continuous emergence of new SARS-CoV-2 variants requires that COVID vaccines be updated to match circulating strains. We generated B/HPIV3-vectored vaccines expressing 6P-stabilized S protein of the ancestral, B.1.617.2/Delta, or B.1.1.529/Omicron variants as pediatric vaccines for intranasal immunization against HPIV3 and SARS-CoV-2 and characterized these in hamsters. Following intranasal immunization, these B/HPIV3 vectors replicated in the upper and lower respiratory tract and induced mucosal and serum anti-S IgA and IgG. B/HPIV3 expressing ancestral or B.1.617.2/Delta-derived S-6P induced serum antibodies that effectively neutralized SARS-CoV-2 of the ancestral and B.1.617.2/Delta lineages, while the cross-neutralizing potency of B.1.1.529/Omicron S-induced antibodies was lower. Despite the lower cross-neutralizing titers induced by B/HPIV3 expressing S-6P from B.1.1.529/Omicron, a single intranasal dose of all three versions of B/HPIV3 vectors was protective against matched or heterologous WA1/2020, B.1.617.2/Delta or BA.1 (B.1.1.529.1)/Omicron challenge; hamsters were protected from challenge virus replication in the lungs, while low levels of challenge virus were detectable in the upper respiratory tract of a small number of animals. Immunization also protected against lung inflammatory response after challenge, with mild inflammatory cytokine induction associated with the slightly lower level of cross-protection of WA1/2020 and B.1.617.2/Delta variants against the BA.1/Omicron variant. Serum antibodies elicited by all vaccine candidates were broadly reactive against 20 antigenic variants, but the antigenic breadth of antibodies elicited by B/HPIV3-expressed S-6P from the ancestral or B.1.617.2/Delta variant exceeded that of the S-6P B.1.1.529/Omicron expressing vector. These results will guide development of intranasal B/HPIV3 vectors with S antigens matching circulating SARS-CoV-2 variants. Author SummaryIntranasal COVID vaccines have the potential to stimulate respiratory mucosal immunity, effectively restricting replication of SARS-CoV-2 in the respiratory tract, thereby reducing virus shedding and transmission. To develop pediatric vaccines for intranasal immunization against HPIV3 and SARS-CoV-2, we use live-attenuated bovine-human parainfluenza virus vaccine, a pediatric intranasal parainfluenza virus vaccine candidate, designed to express the stabilized SARS-CoV-2 spike protein. We compared the immunogenicity and breadth of protection of the B/HPIV3-expressed ancestral, B.1.617.2/Delta, or B.1.1.529/Omicron variants following intranasal immunization in hamsters. All three B/HPIV3 vectors replicated in the respiratory tract, induced mucosal and serum anti-S IgA and IgG, and were protective in the hamster model against matched or heterologous WA1/2020, B.1.617.2/Delta or BA.1 (B.1.1.529.1)/Omicron SARS-CoV-2 challenge. Serum antibodies elicited by all intranasal vaccine candidates were broadly reactive against 20 antigenic variants of SARS-CoV-2, but the antigenic breadth of antibodies elicited by B/HPIV3-expressed stabilized S from the ancestral or B.1.617.2/Delta variant exceeded that of the S-6P B.1.1.529/Omicron expressing vector. Thus, these intranasal vectored SARS-CoV-2 vaccine candidates induce cross-protective SARS-CoV-2 immunity with antigenic breadth similar to that of injectable SARS-CoV-2 vaccines. These results will guide development of intranasal COVID vaccines based on B/HPIV3 vectors with S antigens matching current SARS-CoV-2 variants.