Adenovirus Vector Vaccine Shows Promise Against SARS-CoV-2

A single injection of the Ad5-vectored COVID-19 vaccine induced specific immune responses to the spike glycoprotein at day 28.

Experts from various universities and health agencies in China publishing in The Lancet have explicated results from the first randomized controlled trial evaluating a non-replicating Ad5-vectored SARS-CoV-2 vaccine candidate.

Authors of the study wrote that a single injection of the Ad5-vectored COVID-19 vaccine induced specific immune responses to the spike glycoprotein at day 28.

The phase 2 trial was designed to advance general knowledge on the early-stage experimental vaccine candidate, using an efficacy trial conducted among a large base of patients.

In the study groups, a single injection of the Ad5-vectored COVID-19 vaccine at 1×10¹¹ viral particle and 5×10¹⁰ viral particle doses sparked similar specific immune responses to the coronavirus’ spike glycoprotein at day 28.

The vaccine also appears to have catalyzed seroconversion of neutralizing antibodies in 59% and 47% of participants, and seroconversion of binding antibody in 96% and 97% of participants in 1×10¹¹ and 5×10¹⁰ groups respectively.

A total of 603 volunteers were recruited and screened for eligibility between April 11 and 16. Out of these, 95 individuals were excluded.

The 508 eligible participants who consented to be vaccinated were randomly assigned to vaccine or placebo groups. There were 253 participants randomly assigned to the 1×10¹¹ viral particles dose group, 129 to the 5×10¹⁰ viral particles dose group, and 126 to the placebo group.

The mean age in the study groups was 39.7 years, with 309 individuals aged 18—44 years, 134 45–54 years of age, and 65 aged 55 years or older. The gender distribution was evenly split.

Established Ad5 neutralising antibody titres were similar across study groups. The investigators wrote that among the 508 participants, 266 (52%) had high pre-existing immunity and 242 (48%) had low pre-existing immunity to the Ad5 vector.

“Preexisting immunity to the Ad5 vector and increasing age could partially hamper the specific immune responses to vaccination, particularly for the humoral immune responses,” authors noted.

The promising results come as COVID-19 hotspots continue to flare and community spread of SARS-CoV-2 continues among the population. Investigators of the study strongly urged further development of the various vaccine candidates currently under evaluation.

“As long as there is a COVID-19 epidemic in one area in the world, there is a risk of a pandemic.”