CanSino's COVID-19 vaccine candidate shows promise in first published human data

Clinical data published in The Lancet on Friday from a study of 108 participants demonstrated that CanSino Biologic's recombinant adenovirus type-5 (Ad5)-vectored COVID-19 vaccine candidate is tolerable and immunogenic at 28 days post-vaccination. The authors, who noted "to our knowledge, this is the first report on a first-in-human clinical trial of a novel Ad5-vectored COVID-19 vaccine," said the findings warrant further investigation.

The non-randomised Phase I trial, which was conducted in Wuhan, China, involved 108 healthy adults aged between 18 and 60 years, with the average age being about 36 years. Participants were assigned to receive one low, middle or high dose of CanSino's vaccine candidate, with each group containing 36 people. The primary outcome measure was adverse reactions seven days post-vaccination. In addition, safety was assessed over a period of 28 days after vaccination, while the study also looked at neutralising antibody and T-cell responses.

Mild-to-moderate side effects

Researchers reported that the proportion of people in the low-, middle- and high-dose groups who experienced at least one adverse reaction within the first week after vaccination was 83%, 83% and 75%, respectively, with most being mild or moderate in nature. They noted that nine participants in the low-dose group, two in the middle-dose group, and five who were given the high dose had an episode of severe fever, with one person in the high-dose group also experiencing severe symptoms of fatigue, dyspnoea and muscle pain, while another reported severe fatigue and joint pain. The authors said these reactions occurred within 24 hours post-vaccination, and persisted for no more than two days. Meanwhile, no serious adverse event was noted at 28 days post-vaccination.

Sufficient levels of immune response?

Results also showed that neutralising antibodies rose significantly at day 14, and peaked 28 days post-vaccination, while specific T-cell response peaked at day 14 after vaccination. However, the authors acknowledged that it remains unclear what roles specific antibodies or T cells have in building up effective immunity against COVID-19, "therefore, we are unable to predict the protection of the Ad5-vectored COVID-19 vaccine on the basis of the vaccine-elicited immune responses in this study." Researchers say they are now going to follow up the vaccine recipients for at least six months.

CanSino's vaccine, dubbed Ad5-nCoV, received regulatory approval earlier this year for clinical trials in China, and will be tested in Canada as part of a recent agreement with researchers there.

The latest COVID-19 findings follow recent early data released by Moderna for its mRNA-1273 vaccine candidate, which elicited neutralising antibodies in all eight initial participants. While the news drove up shares the day it came out, a report highlighting the early nature of the data for mRNA-1273 pulled down the stock value a day later.

Meanwhile preclinical results recently published in Nature Communications demonstrated that Inovio Pharmaceuticals' DNA vaccine candidate INO-4800 induced neutralising antibodies and T-cell responses against SARS-CoV-2 in mice and guinea pigs, while preliminary safety data from an ongoing Phase I trial indicate the experimental vaccine appears safe in humans as well (for related analysis, see Inovio takes preclinical vaccine data to the bank).

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