One dose of the Ad5-nCoV COVID-19 vaccine is 57.5% effective against symptomatic infection and 91.7% effective against severe disease after 28 days of vaccination, researchers report today.
A phase 3 randomised control trial analysis of the vaccine, which was developed in China, also showed there were no reports of vaccine-related serious adverse events and that most adverse events, including injection-site pain, headache, drowsiness, and general muscle aches, were mild to moderate.
The vaccine, which was developed by CanSino Biologics, Inc. and the Beijing Institute of Biotechnology, is a single-dose viral vector vaccine that can be stored between 2C and 8C. It has been approved for emergency use in 10 countries, including Argentina, Chile, Mexico, and Pakistan, where the phase 3 trial took place.
Study lead author Dr Scott Halperin, from Dalhousie University, Canada, said: “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 hospitalisation.
“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.”
Details of the trial, which is ongoing, are published in today’s edition of *The Lancet*.
It began on September 22, 2020, and, by January 15, 2021, had enrolled 36,982 over 18s, of whom 36,727 were randomised to receive either a vaccine or placebo across 66 sites at centres in Argentina, Chile, Mexico, Pakistan and Russia.
The research team carried out an efficacy analysis once the protocol threshold of 150 laboratory-confirmed symptomatic COVID-19 at 28 days post-injection was reached on January 15, 2021. At this point, there were 21,250 trial participants in the primary efficacy cohort.
In the placebo group, there were 105 positive COVID-19 cases out of 10,590 participants and 45 positive COVID-19 cases out of 10,660 participants in the vaccine group. This equates to an efficacy of 57.5% at 28 days post-vaccination.
They team reports efficacy against severe disease was 91.7% at 28 days post-vaccination, which was defined as a minimum of one 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.
Ad5-nCoV was found to be well tolerated and produced high levels of anti-RBD antibodies and neutralising antibodies.
However, the authors say that because the efficacy analysis was conducted in samples collected on or before January 15, 2021, they do not know its effectiveness on variants of concern, such as delta and omicron.
Dr Joanne Langley, of Dalhousie University, added: “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.”
Research is now taking place to determine the vaccine’s long-term safety and effectiveness as well as its effectiveness against delta, omicron and other variants of concern, while studies are taking place into a potential booster dose.
Halperin SA, Ye L, MacKinnon-Cameron D et al. Final efficacy analysis, interim safety analysis, and immunogenicity of a single dose of recombinant novel coronavirus vaccine (adenovirus type 5 vector) in adults 18 years and older: an international, multicentre, randomised, double-blinded, placebo-controlled phase 3 trial. *The Lancet* 24 December 2021
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