HealthDay News – The nonreplicating adenovirus type-5 (Ad5)-vectored COVID-19 vaccine appears safe and induces immune responses at a dose of 5×1010 viral particles, according to a study published online July 20 in The Lancet.

Feng-Cai Zhu, from Jiangsu Provincial Center for Disease Control and Prevention in Nanjing, China, and colleagues conducted a randomized double-blind, placebo-controlled, phase 2 trial of the Ad5-vectored COVID-19 vaccine in Wuhan. Healthy adults were eligible to participate and were randomly assigned to receive either the vaccine at a dose of 1×1011 viral particles per mL or 5×1010 viral particles per mL or placebo in a 2:1:1 ratio (253, 129, and 126 participants, respectively).

The researchers found that at day 28, the receptor binding domain-specific enzyme-linked immunosorbent assay antibodies peaked at 656.5 and 571.0, with seroconversion rates of 96 and 97%, respectively, for the 1×1011 and 5×1010 viral-particle dose groups. Significant neutralizing antibody responses were induced to live severe acute respiratory syndrome coronavirus 2, with geometric mean titers of 19.5 and 18.3 for participants receiving 1×1011 and 5×1010 viral particles, respectively. Specific interferon γ enzyme-linked immunospot assay responses after vaccination were observed in 90 and 88% of participants, respectively. Solicited adverse reactions were reported in 72 and 74% of participants, respectively, with severe adverse reactions in 9 and 1%, respectively.

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“The results support testing of the Ad5-vectored COVID-19 vaccine at 5 ×1010 viral particles in a phase 3 effectiveness trial in healthy adults,” the authors write.

One author disclosed financial ties to CanSino Biologics, which is a developer of the vaccine and partially funded the study.

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