RESUMO
An intranasal COVID-19 vaccine, DelNS1-based RBD vaccines composed of H1N1 subtype (DelNS1-nCoV-RBD LAIV) was developed to evaluate the safety and immunogenicity in healthy adults. We conducted a phase 1 randomized, double-blinded, placebo-controlled study on healthy participants, age 18-55 and COVID-19 vaccines naïve, between March and September 2021. Participants were enrolled and randomly assigned (2:2:1) into the low and high dose DelNS1-nCoV-RBD LAIV manufactured in chicken embryonated eggs or placebo groups. The low and high-dose vaccine were composed of 1 × 107 EID50/ dose and 1 × 107.7 EID50/ dose in 0.2 mL respectively. The placebo vaccine was composed of inert excipients/dose in 0.2 mL. Recruited participants were administered the vaccine intranasally on day 0 and day 28. The primary end-point was the safety of the vaccine. The secondary endpoints included cellular, humoral, and mucosal immune responses post-vaccination at pre-specified time-points. The cellular response was measured by the T-cell ELISpot assay. The humoral response was measured by the serum anti-RBD IgG and live-virus neutralizing antibody against SARS-CoV-2. The saliva total Ig antibody responses in mucosal secretion against SARS-CoV-2 RBD was also assessed. Twenty-nine healthy Chinese participants were vaccinated (low-dose: 11; high-dose: 12 and placebo: 6). The median age was 26 years. Twenty participants (69%) were male. No participant was discontinued due to an adverse event or COVID-19 infection during the clinical trial. There was no significant difference in the incidence of adverse events (p = 0.620). For the T-cell response elicited after full vaccination, the positive PBMC in the high-dose group increased to 12.5 SFU/106 PMBC (day 42) from 0 (baseline), while it increased to 5 SFU/106 PBMC (day 42) from 2.5 SFU/106 PBMC (baseline) in the placebo group. The high-dose group showed a slightly higher level of mucosal Ig than the control group after receiving two doses of the vaccine (day 31, 0.24 vs. 0.21, p = 0.046; day 56 0.31 vs. 0.15, p = 0.45). There was no difference in the T-cell and saliva Ig response between the low-dose and placebo groups. The serum anti-RBD IgG and live virus neutralizing antibody against SARS-CoV-2 were undetectable in all samples. The high-dose intranasal DelNS1-nCoV-RBD LAIV is safe with moderate mucosal immunogenicity. A phase-2 booster trial with a two-dose regimen of the high-dose intranasal DelNS1-nCoV-RBD LAIV is warranted.
RESUMO
Porcine circovirus type 2 (PCV2) belongs to the family Circoviridae, and is the causative agent of post-weaning multisystemic wasting syndrome (PMWS) in pigs. In this study, phylogenetic analyses of three complete PCV2 genomic sequences from Hong Kong suggest that natural recombination happened among different lineages of PCV2. A preliminary investigation of the parental strains of these potential recombinants was carried out using bootscanning. Statistical significance of this recombination event was tested and positions of the potential recombination breakpoints were estimated in a maximum-likelihood framework. The recombinant breakpoints were estimated to be located within the origin of replication (ori) and replicase (rep) gene of PCV2. Interestingly, several GenBank sequences of PCV2 in mainland China were found to have a recombination pattern similar to that of the potential PCV2 recombinants from Hong Kong, implying that this recombinant genotype might already be widespread within mainland China.