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Ad5-nCoV COVID-19 Vaccine is Safe and Efficacious

A phase 3 trial shows one dose is 91.7 % effective against severe disease.



A single dose of the Ad5-nCoV (Convidecia) COVID-19 vaccine is 57.5% effective against symptomatic COVID-19 and 91.7% effective against severe disease beginning 28 days postvaccination, a phase 3 trial demonstrated. The vaccine was developed in China and the results were published in The Lancet.

“Our study suggests that one dose of Ad5-nCoV is highly effective against severe disease— potentially helping to ease the tremendous strain COVID-19 has put on health systems around the world by keeping people from becoming seriously ill or requiring hospitalization,"study lead author Scott Halperin, MD, Dalhousie University, Canada, said. "In addition, because the vaccine is effective against severe disease after one injection, it could help provide improved access to vaccination, especially in low- and middle-income countries, where it can be more challenging to reach people with a two-dose primary vaccination course.”

The study investigators randomized 36,727 participants to receive either the investigational vaccine or placebo across 66 enrolment sites including Argentina, Chile, Mexico, Pakistan, and Russia. The researchers conducted an efficacy analysis once the protocol threshold of 150 laboratory-confirmed (RT-PCR positive) symptomatic COVID-19 at 28 days post-injection was reached on January 15, 2021. The investigators pointed out there were 21,250 trial participants in the primary efficacy cohort, and they reported 105 positive COVID-19 cases out of 10,590 participants in the placebo group and 45 positive COVID-19 cases out of 10,660 participants in the vaccine group, resulting in an efficacy of 57.5% at 28 days postvaccination.

In looking at efficacy against severe disease, they reported it was 91.7% effective at 28 days post-vaccination. Severe disease was defined as a minimum of 1 of clinical signs at rest indicative of severe systemic illness, respiratory failure, evidence of shock, significant acute renal, hepatic, or neurologic dysfunction, or admission to an ICU. There were no COVID-19-related deaths among vaccine recipients.

In terms of safety, no vaccine-related serious adverse events were reported, and most adverse events, including injection-site pain, headache, drowsiness, and generalized muscle aches, were mild to moderate.

The study’s authors caution that the efficacy analysis was conducted in samples collected on or before January 15, 2021, and do not include recent variants of concern such as the Delta and Omicron variants.

“More research is needed to determine Ad5-nCoV’s effectiveness and durability over a longer period of time as well as its effectiveness against variants of concern, including omicron, which is rapidly overtaking delta as the dominant strain worldwide,” says Joanne Langley, MD, Dalhousie University, Canada.

The authors also point out the study is still ongoing,