Vaccination with Adenovirus Type 5 Vector-Based COVID-19 Vaccine as the Primary Series in Adults: A Randomized, Double-Blind, Placebo-Controlled Phase 1/2 Clinical Trial.

This randomized, double-blind, placebo-controlled phase 1/2 trial aimed at evaluating the safety and immunogenicity of Ad5-nCoV via aerosolized or intramuscular or intramuscular-aerosolized routes in SARS-CoV-2-negative adults aged over 18 years. In the phase 1 trial, participants were sequentially enrolled into one of five regimen cohorts: Low-Dose (two doses of aerosolized Ad5-nCoV with 0.5 × 10 viral particles [vps] per dose), Middle-Dose (two doses of aerosolized Ad5-nCoV with 1.0 × 10 vps per dose), High-Dose (two doses of aerosolized Ad5-nCoV with 2.0 × 10 vps per dose), Mixed (intramuscular Ad5-nCoV with 5.0 × 10 vps [first dose] and aerosolized Ad5-nCoV with 2.0 × 10 vps [second dose]), and Single-Dose (one dose of aerosolized Ad5-nCoV with 1.0 × 10 vps). Eligible participants in the phase 2 trial were stratified by 18-59 years old or ≥60 years old and then were sequentially enrolled into one of six regimen cohorts: Low-Dose, Middle-Dose, High-Dose, Mixed, Single-Dose, and Intramuscular (one dose of intramuscular Ad5-nCoV with 1.0 × 10 vps). The intervals between the two doses were 56 days. Participants were randomly allocated in 3:1 (phase 1) and 5:1 (phase 2) ratios to receive either Ad5-nCoV or the placebo in each cohort. This study is registered on ClinicalTrials.gov, NCT04840992. Most adverse reactions that occurred during the solicited period were mild and moderate. One serious adverse event (myelodysplastic syndrome) was considered potentially related to the aerosolized Ad5-nCoV. The GMTs of neutralizing antibodies in the Mixed group were the highest with 57.03 (95% CI: 23.95, 135.80) and 97.37 (95% CI: 74.30, 127.59) in phase 1 and 2 trials, respectively, 28 days after the second dose ( < 0.0001), which showed significantly higher immune responses compared to other regimens with aerosolized or intramuscular Ad5-nCoV alone.