A Phase 1, Randomized, Double-Blinded, Placebo-Controlled and Dose-Escalation Study to Evaluate the Safety and Immunogenicity of the Intranasal DelNS1-nCoV-RBD LAIV for COVID-19 in Healthy Adults

Abstract

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 × 10^7.7 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.

Keywords: COVID-19; DelNS1-nCoV-RBD LAIV; intranasal; phase-1.

Figure 1

A sample of the intranasal DelNS1-nCoV-RBD LAIV.

Figure 2

Overview of participants’ allocation. High-dose: DelNS1-nCoV-RBD LAIV (1 × 10^7.7 EID₅₀/dose) in 0.2 mL. Low-dose: DelNS1-nCoV-RBD LAIV (1 × 10⁷ EID₅₀/dose) in 0.2 mL. Placebo: inert excipients/dose in 0.2 mL.

Figure 3

Reactogenicity events reported for the 14-day period after each vaccination with DelNS1-nCoV-RBD LAIV. Subjects received two doses of test vaccine or placebo on day 1 and day 29, and were then required to record any AE in the diary for a 14-day period after each vaccination. (A) AE occurred in subjects after the first vaccination. (B) AE occurred in subjects after the second dose. Fisher’s exact test was used to analyze the AEs in the three groups.

Figure 4

T-cell responses by ELISpot over time. Blood samples were taken from the subjects on baseline (day 0) and at 7, 14, 28, 35, and 42 days after the first dose of vaccine. Once separated from the blood, PBMC were seeded into anti-human IFN-γ antibody coated plate followed by the incubation with SARS-CoV-2 RBD peptide pool overnight. The substrate was added into the plate after cells incubated with Streptavidin-Alkaline Phosphatase (ALP). The spots in the plate were counted under an immunospot reader. One-way ANOVA was used to compare the T-cell response in the three groups. The error bars represent median with interquartile ranges (IQR).

Figure 5

Total saliva Ig titre over time. Saliva samples were collected at baseline (day 0) and at 3, 28, 31, and 56 days after the first vaccination. After being treated with 1% Triton-100 for 30 min, saliva was diluted 2 folds with PBS. Biotinylated recombinant SARS-CoV-2 RBD was added into the 96-well plate coated with avidin for a 30 min-incubation. Then, treated saliva samples were added into the wells. After 1 h, the plate was incubated with horseradish peroxidase (HRP) conjugated goat anti-human IgG, IgM, and IgA antibody. Finally, the optical density (OD) was read at 450 and 620 nm. One-way ANOVA was used to compare the mucosal Ig response in the three groups.