Safety and Immunogenicity of a Recombinant Adenovirus Type-5–Vectored Coronavirus Disease 2019 (COVID-19) Vaccine With a Homologous Prime-Boost Regimen in Healthy Participants Aged ≥6 Years: A Randomized, Double-Blind, Placebo-Controlled, Phase 2b Trial

Abstract

Background We assessed the safety and immunogenicity of a recombinant adenovirus type-5 (Ad5)-vectored COVID-19 vaccine with homologous prime-boost regimens in healthy participants aged 6 years and above. Methods In this randomised, double-blind, placebo-controlled trial, participants received low-dose vaccine, middle-dose vaccine or placebo. Prime-booster regimens were given intramuscularly 56 days apart. ELISA antibodies to the receptor binding domain (RBD) and pseudovirus neutralising antibodies were detected. Adverse events were monitored for 28 days following each vaccination. Results A total of 430 participants were enrolled in the study, with 30 participants aged 18-55 years (MID cohort), 250 participants aged 56 years and older (OLD cohort), and 150 participants aged 6-17 years (MIN cohort). Ad5-vectored COVID-19 vaccine induced significant RBD-specific ELISA antibodies which decreased with increasing age, with geometric mean titres (GMTs) of 1037.5 in MIN cohort, 647.2 in MID cohort, and 338.0 in OLD cohort receiving 5×10 10 viral particles on day 28 following boost vaccination. Pseudovirus neutralising antibodies showed a similar pattern, with GMTs of 168.0 in MIN cohort, 76.8 in MID cohort, and 79.7 in OLD cohort. A single dose in children and adolescents induced higher antibody responses than that elicited by two doses in adults, with GMTs of 1091.6 and 96.6 in ELISA antibody and neutralising antibody, respectively. Homologous prime-boost vaccination was safety and tolerable. Conclusions Ad5-vectored COVID-19 vaccine with a single dose was safe and induced robust immune responses in children and adolescents aged 6-17 years. A prime-boost regimen needs further exploration for Ad5-vectored COVID-19 vaccine.

Immune Evasive Effects of SARS-CoV-2 Variants to COVID-19 Emergency Used Vaccines

“…The antibody response induced by Ad5-nCoV vaccine peaked on day 28 post-vaccination and the specific T-cell response peaked on 14 days post-vaccination in adults aged between 18 and 60 years ( 117 ). Based on this promising result from the first human trials, CanSino conducted further investigations in a broad range of age groups, in which showed that administration with prime-boost regimen in children and adolescents aged 6-17 years (GMTs: 1037.5) produced higher levels of immune responses than adults aged 18-55 years (GMTs: 647.2) and those aged 56 years and older (GMTs: 338.0) ( 118 ). Consistent with this study, the level of immune response to the vaccine declined significantly with age in adults aged 18 years and older, and that was severely affected by the pre-existing high anti-Ad5 immunity ( 119 ).…”

Chinese Parent Intention to Vaccinate Children With Special Diseases Against COVID-19

“…Currently, the COVID-19 vaccine is administered to adults aged 18 years in China ( 6 ). In terms of the development of the global pandemic, the proportion of cases in children showed an increasing trend ( 7 ).…”

Safety and efficacy of the COVID-19 vaccine in children and/or adolescents:A meta-analysis

“…Table 1 describes the detailed characteristics of the effectiveness and safety studies. 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 Seven studies have shown that the overall effectiveness of the COVID-19 vaccine is 96.09% (95% confidence interval [CI]:93.35–98.90, p<0.01) ( Figure. 1 A), of the attenuated vaccine is 95.05% (95% [CI]:90.21-100.16, p<0.01) ( Figure.…”