THURSDAY, July 23, 2020 (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 percent, 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 percent of participants, respectively. Solicited adverse reactions were reported in 72 and 74 percent of participants, respectively, with severe adverse reactions in 9 and 1 percent, respectively.

“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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