Co-administration of intranasal parainfluenza virus vaccines expressing antigenically distinct SARS-CoV-2 S antigens elicits broad and durable immunity in hamsters

Intranasal COVID-19 vaccines with the ability to induce broad and durable mucosal and systemic immunity would be useful as stand-alone vaccines or in combination with injectable vaccines. Here, we evaluated in the hamster model the immunogenicity, breadth of immunity, and durability of protection elicited by co-administration of two live-attenuated bovine/human parainfluenza virus type 3 (B/HPIV3) vectors expressing antigenically distinct prefusion stabilized S proteins of the ancestral SARS-CoV-2 isolate (B/HPIV3/S-6P) or the Omicron/BA.5 variant (B/HPIV3/S-BA.5-2P). These vectors are being developed as bivalent pediatric vaccines against HPIV3 and SARS-CoV-2 and are based on bovine PIV3 with the fusion (F) and hemagglutinin-neuraminidase (HN) glycoproteins replaced by those of human PIV3. To broaden the S-specific antibody response, we evaluated co-administration of these B/HPIV3 S-expressing vectors. Each B/HPIV3 S-expressing vector induced robust serum anti-S IgG and IgA antibody levels to the antigen-matched S protein that were sustained for at least five months. Co-administration increased the breadth of the S-specific antibody response, spanning the antigenic breadths of the response elicited by each B/HPIV3 S-expressing vector individually. Animals that had received the mixture of vectors developed neutralizing antibodies to ancestral as well as recently circulating SARS-CoV-2 strains. Hamsters immunized intranasally were protected against Omicron/BA.5 challenge 5 months after immunization, with no weight loss, SARS-CoV-2 challenge virus replication, or increase in host inflammatory cytokines in the upper and lower airways detectable after the challenge, indicating durable protection. Thus, intranasal co-administration of live-attenuated B/HPIV3 expressing antigenically distinct S proteins induced broad and durable antibody responses and long-term protection against Omicron/BA.5 challenge. This approach warrants further development and may better protect against emerging SARS-CoV-2 variants.